NAME

ODF::lpOD::Table - Table management

DESCRIPTION

The present manual page introduces the way lpOD allows the user to handle ODF tables and their components, namely the columns, rows and cells.

The lpOD API doesn't make differences between document types in this area. So, tables are dealed with in the same way for a spreadsheet document (whose content is just a set of tables) as for any other document.

A table is an instance of the lpOD odf_table class.

An odf_table object is a structured container that holds two sets of objects, a set of rows and a set of columns, and that is optionally associated with a table style.

The basic information unit in a table is the cell. Every cell is contained in a row. Table columns don't contain cells; an ODF column holds information related to the layout of a particular column at the display time, not content data.

A cell can directly contain one or more paragraphs. However, a cell may be used as a container for high level containers, including lists, tables, sections and frames.

Every table is identified by a name (which must be unique for the document) and may own some optional properties.

Table creation and retrieval

Like any other odf_element table may be created either from scratch according to various parameters or by cloning an existing table using the generic clone method of odf_element. The second way is the most recommended one because, while it looks very easy to create a table with a default appearance, a typical convenient layout may require a lot of style definitions and is much more difficult to specify by program than through a point-and-click interface.

A table is created using odf_create_table with a mandatory name as its first argument and the following optional parameters:

width, length: the initial size of the new table (rows and columns), knowing that it's zero-sized by default (beware: because cells are contained in rows, no cell is created as long as width is less than 1);

size: specifies a length and a width (in this order) as a single string (the two values are comma-separated); may replace length and width;

style: the name of a table style, already existing or to be defined;

cell style: the style to use by default for every cell in the table;

protected: a boolean that, if TRUE, means that the table should be write-protected when the document is edited through a user-oriented, interactive application (of course, such a protection doesn't prevent an lpOD-based tool from modifying the table)(default is FALSE);

protection key: a (supposedly encrypted) string that represents a password; if this parameter is set and if protected is TRUE, a end-user interactive application should ask for a password that matches this string before removing the write-protection (beware, such a protection is not a security feature);

print: boolean, tells that the table should be printable; default is TRUE;

print ranges: the cell ranges to be printed, if some areas are not to be printed; the value of this parameter is a space-separated list of cell ranges expressed in spreadsheet-style format (ex: "E6:K12").

Once created, a table may be incorporated somewhere using insert_element of append_element, like any other odf_element.

Caution: a table should not be inserted in any context. For example, a table should not be inserted within a paragraph. A bad placement may corrupt the document structure. Right contexts are, for example, the document body (in a spreadsheet or text document), a section (in a text document) or a table cell (knowing that the ODF standard allows nested tables).

The style of a table may be retrieved at any time using the generic get_style and set_style accessors.

A table may be retrieved in a document according to its unique name using the context-based get_table_by_name with the name as argument. It may be selected by its sequential position in the list of the tables belonging to the context, using get_table_by_position, with a zero-based numeric argument (possibly counted back from the end if the argument is negative). A get_table() method is provided, that works like get_table_by_position() if the argument is numeric or like get_table_by_name() otherwise (of course, if the name of the desired table looks like a number, there is no choice but get_table_by_name() to retrieve it by name). Without argument, get_table() returns the first table in the context (if any). In addition, it's possible to retrieve a table according to its content, through get_table_by_content; this method returns the first table (in the order of the document) whose text content matches the given argument, which is regarded as a regular expression.

Table content retrieval

A table object provides methods that allow to retrieve any column, row or cell using its logical position. A position may be expressed using either zero-based numeric coordinates, or alphanumeric, spreadsheet-like coordinates. For example the top left cell should be addressed either by (0,0) or by "A1". On the other hand, numeric coordinates only allow the user to address an object relatively to the end of the table; for example, (-1,-1) designates the last cell of the last row whatever the table size.

Table object selection methods return a null value, without error, when the given address is out of range.

The number of rows and columns may be got using the odf_table get_size method.

An individual cell is selected using get_cell with either a pair of numeric arguments corresponding to the row then the column, or an alphanumeric argument whose first character is a letter. The second argument, if provided, is ignored as soon as the first one begins with a letter.

The two following instructions are equivalent and return the second cell of the second row in a table (assuming that $t is a previously selected table):

        $cell = $t->get_cell('B2');
        $cell = $t->get_cell(1, 1);

get_row() allows the user to select a table row as an ODF element. This method requires a zero-based numeric value.

get_column() works according to the same logic and returns a table column ODF element.

The full set of row and column objects may be selected using the table-based get_rows() and get_columns() methods. By default these methods return repectively the full list of rows or columns. They can be restricted to a specified range of rows or columns. The restriction may be expressed through two numeric, zero-based arguments indicating the positions of the first and the last item of the range. Alternatively, the range may be specified using a more "spreadsheet-like" syntax, in only one alphanumeric argument representing the visible representation of the range through a GUI; this argument is the concatenation of the visible numbers of the starting and ending elements, separated by a ":", knowing that "1" is the visible number of the row zero while "A" is the visible number or the column zero. As a consequence, the two following instructions are equivalent and return a list including the rows from 5 to 10 belonging to the table t:

        @rows = $t->get_rows(5, 10);
        @rows = $t->get_rows('6:11');

According to the same logic, each of the two instruction below returns the columns from 8 to 15::

        @cols = $t->get_columns(8, 15);
        @cols = $t->get_columns('I:P');

Once selected, knowing that cells are contained in rows, a row-based get_cell() method is provided. When called from a row object, get_cell() requires the same parameter as the table-based get_column() method. For example, the following sequence returns the same cell as in the previous example:

        $r = $t->get_row(1);
        $c = $r->get_cell(1);

Cell range selection

get_cells extracts rectangular ranges of cells in order to allow the applications to store and process them out of the document tree, through regular 2D tables. The range selection is defined by the coordinates of the top left and the bottom right cells of the target area. get_cells allows two possible syntaxes, i.e. the spreadsheet-like one and the numeric one. The first one requires an alphanumeric argument whose first character is a letter and which includes a ':', while the second one requires four numeric arguments. As an example, the two following instructions, which are equivalent, return a bi-dimensional array corresponding to the cells of the B2:D15 area of a table:

        @cells = $table->get_cells("B2:D15");
        @cells = $table->get_cells(1,1,14,3);

Note that, after such a selection, $cells[0][0] contains the "B2" cell of the ODF table.

If get_cells is called without argument, the selection covers the whole table.

A row object has its own get_cell() method. The row based version of get_cells() returns, of course, a one-row table of cell objects. When used without argument, it selects all the cells of the row. It may be called with either a pair of numeric arguments that represent the start and the end positions of the cell range, or an alphanumeric argument (whose the numeric content is ignored and should be omitted) corresponding to the start and end columns in conventional spreadsheet notation. The following example shows two ways to select the same cell range (beginning at the 2nd position and ending at the 26th one) in a previously selected row:

        @cells = $r->get_cells('B:Z');
        @cells = $r->get_cells(1, 25);

The elements of the Perl table returned by get_cells are references to the cells of the ODF table (not copies); the Perl table just maps an ODF table area, and any cell property change made through this Perl table affects the underlying ODF cell.

Row and column customization

The objects returned by get_row and get_column can be customized using the standard set_attribute or set_attributes method. Possible attributes are:

• default cell style name: the default style which apply to each cell in the column or row unless this cell has no defined style attribute;

• visibility: specifies the visibility of the row or column; legal values are 'visible', 'collapse' and 'filter'.

The style may be get or set using get_style or set_style.

Table expansion

A table may be expanded vertically and horizontally, using its add_row and add_column methods.

add_row allows the user to insert one or more rows at a given position in the table. The new rows are copies of an existing one. Without argument, a single row is just appended as the end. A number named parameter specifies the number of rows to insert.

An optional before named parameter may be provided; if defined, the value of this parameter must be a row number (in numeric, zero-based form) in the range of the table; the new rows are created as clones of the row existing at the given position then inserted at this position, i.e. before the original reference row. A after parameter may be provided instead of before; it produces a similar result, but the new rows are inserted after the reference row. Note that the two following instructions produce the same result (assuming $t is a previously selected or created table):

        $t->add_row(number => 1, after => -1);
        $t->add_row();

The inserted rows are initialized as clones of the row used as the reference through the after or before or of the last existing row if the new row in appended at the end. So the new rows (and their cells) inherit the same style and content as an existing one.

The add_column method does the same thing with columns as add_row for rows. However, because the cells belong to rows, it works according to a very different logic. add_column inserts new column objects (clones of an existing column), then it goes through all the rows and inserts new cells (cloning the cell located at the reference position) in each one.

Of course, it's possible to use insert_element in order to insert a row, a column or a cell externally created (or copied from an other table from another document), provided that the user carefully checks the consistency of the resulting contruct. As an example, the following sequence appends a copy of the first row of $t1 after the 5th row of $t2:

   $to_be_inserted = $t1->get_row(0)->clone;
   $t2->insert_element($to_be_inserted, after => $t2->get_row(5));

While a table may be expanded vertically using add_row, each row may be expanded using the odf_row add_cell method whose parameters and behaviour are the same as the table-based add_row method.

Row and column group handling

The content expansion and content selection methods above work with the table body. However it's possible to manage groups of rows or columns. A group may be created with existing adjacent rows or columns, using set_row_group() and set_column_group() respectively. These methods take two arguments, which are the numeric positions of the starting and ending elements of the group. However, these numeric arguments may be replaced by a single alphanumeric range definition argument, so the following instructions are equivalent; both create a group including the same 3 columns ("C" to "E"):

        $column_group = $table->set_column_group(3, 5);
        $column_group = $table->set_column_group("C:E");

The same idea apply to row groups; however, beware that in range alphanumeric notation, the numbers represents the spreadsheet end-user point of view, so they are one-based; as an example, the two following instructions, that create a row group including the rows 3 to 5, are equivalent:

        $row_group = $table->set_row_group(3, 5);
        $row_group = $table->set_row_group("4:6");

In addition, an optional display named boolean parameter may be provided (default=TRUE), instructing the applications about the visibility of the group.

Both set_row_group() and set_column_group() return an object which can be used later as a context object for any row, column or cell retrieval or processing. An existing group may be retrieved according to its numeric position using get_row_group() or get_column_group() with the position as argument, or without argument to get the first (or the only one) group.

A group can't bring a particular style; it's just visible or not. Once created, its visibility may be turned on and off by changing its display value through set_attribute().

Knowing that cells depends on rows, a row group provides the same get_cell() method as a table. It provides a get_row() method, while a column group provides a get_column() one.

A row group provides a add_row() method, while a column group provides a add_column() method. These methods work like their table-based versions, and they allow the user to expand the content of a particular group.

Row and column group may be collapsed or expanded using their collapse() and uncollapse() methods.

Table headers

One or more rows or columns in the beginning of a table may be organized as a header. Row and columns headers are created using the set_row_header() and set_column_header() table-based methods, and retrieved using get_row_header() and get_column_header(). A row header object brings its own add_row() method, which works like the table-based add_row() but appends the new rows in the space of the row header. The same logic applies to column headers which have a add_column() method. An optional positive integer argument may specify the number or rows or columns to include in the header (default=1).

Note that a column header is a row or a set of rows containing column titles that should be automatically repeated on every page if the table does not fit on a single page, while a row headers is a column or a set of columns containing row titles. In the present version, row headers are not fully supported.

A table can't directly contain more than one row header and one column header. However, a column group can contain a column header, while a row group can contain a row header. So the header-focused methods above work with groups as well as with tables.

A table header doesn't bring particular properties; it's just a construct allowing the author to designate rows and columns that should be automatically repeated on every page if the table doesn't fit on a single page.

The ``get_xxx()`` table-based retrieval methods ignore the content of the headers. However, it's always possible to select a header, then to used it as the context object to select an object using its coordinates inside the header. For example, the first instruction below gets the first cell of a table body, while the third and third instructions select the first cell of a table header::

   c1 = table.get_cell(0,0)
   header = table.get_header()
   c2 = header.get_cell(0,0)

Individual cell property handling

A cell owns both a content and some properties which may be processed separately.

The cell content is a list of one or more ODF elements. While this content is generally made of a single paragraph, it may contain several paragraphs and various other objects. The user can attach any content element to a cell using the standard insert_element method. However, for the simplest (and the most usual) cases, it's possible to use set_text. The cell-based set_text method diffs from the generic odf_element set_text: it removes the previous content elements, if any, then creates a single paragraph with the given text as the new content. In addition, this method accepts an optional style named parameter, allowing the user to set a paragraph style for the new content. To insert more content (i.e. additional paragraphs and/or other ODF elements), the needed objects have to be created externally and attached to the cell using insert_element or append_element. Alternatively, it's possible to remove the existing content (if any) and attach a full set of content elements in a single instruction using set_content; this last cell method takes a list of arbitrary ODF elements and appends them (in the given order) as the new content.

The get_content cell method returns all the content elements as a list. For the simplest cases, the cell-based get_text method directly returns the text content as a flat string, without any structural information and whatever the number and the type of the content elements.

The cell properties may be read or changes using get_xxx and set_xxx methods, where xxx stands for one of the following:

• style: the name of the cell style;

• type: the cell value type, which may be one of the ODF supported data types, used when the cell have to contain a computable value (may be omitted with text cells, knowing that the default type is 'string');

• value: the numeric computable value of the cell, used when the type is defined;

• currency: the international standard currency unit identifier (ex: EUR, USD), used when the type is 'currency';

• formula: a calculation formula whose result is a computable value (the grammar and syntax of the formula is application-specific and not ckecked by the lpOD API (it's stored as flat text and not interpreted);

• protect: boolean (default FALSE), tells the applications that the cell can't be edited.

If set_currency is used with a non-null value, then the type of the cell is automatically set to 'currency'. If set_type forces a type that is not 'currency', then the cell currency is unset.

Cell span expansion

A cell may be expanded in so it covers one or more adjacent columns and/or rows. The cell-based set_span() method allows the user to control this expansion. It takes rows and columns as parameters, specifying the number of rows and the number of columns covered. The following example selects the "B4" cell then expands it over 4 columns and 3 rows:

        $cell = $table->get_cell('B4');
        $cell->set_span(rows => 3, columns => 4);

The existing span of a cell may be get using get_span(), which returns the rows and columns values.

This method changes the previous span of the cell. The default value for each parameter is 1, so a set_span() without argument reduces the cell at its minimal span.

When a cell is covered due to the span of another cell, it remains present and holds its content and properties. However, it's possible to know at any time if a given cell is covered or not through the boolean is_covered() cell method. In addition, the span values of a covered cell are automatically set to 1, and set_span() is forbidden with covered cells.

Performance issues

The table-oriented access methods perform relatively well against tables including up to thousands, if not tens of thousands of cells. So there is no performance issue with tables belonging to text documents. On the other hand, spreadsheet documents may contain tables whose size in potentially unlimited. As soon as you are faced to wrong response times and overloaded CPUs, you may consider using the following workarounds, which can (sometimes) improve the performances, possibly at the cost of a reduced functionality.

Accessing cells from rows

Remember that cells belong to rows and rows belong to tables. As a consequence, accessing a cell is faster from the row than from the table. So, each time you need to get several cells belonging to the same row, you should first get the row then use it as the context for subsequent cell accesses. As an illustration, each of the two following code snippets scans a whole table and loads the text of every cell in a list, but the second one is faster:

        # table scan, way 1
        my @text = ();
        my ($l, $w) = $table->get_size;
        for (my $i = 0 ; $i < $l ; $i++) {
                for (my $j = 0 ; $j < $w ; $j++) {
                        push @text, $table->get_cell($i, $j)->get_text;
                        }
                }

        # table scan, way 2
        my @text = ();
        my ($l, $w) = $table->get_size;
        for (my $i = 0 ; $i < $l ; $i++) {
                my $row = $table->get_row($i);
                for (my $j = 0 ; $j < $w ; $j++) {
                        push @text, $row->get_cell($j)->get_text;
                        }
                }

At a higher level but for the same reasons, get_cell() and get_cells() are slower as column group methods that as table or row group methods. In other words, when a cell belongs to the intersection of a row group and a column group, it may be accessed faster from the table or the row group than from the column group.

Mapping ODF tables with Perl lists

Thanks to get_cells(), you can easily associate a Perl table to a selected area in a document table. As an example, the following instruction produces a 2D Perl list that maps the "B4:Z50" area in a given table:

        my @cells = $table->get_cells("B4:Z50");

While get_cells() is a costly method, it provides an array of pre-selected cells. Beware that get_cells() return the cells themselves, not copies, so, after the instruction above, $cells[0][0] is the "B4" cell of the ODF table, while $cells[-1][-1] is the "Z50" cell, and so on. As a consequence, the 2 instructions below are functionally equivalent, but the second one in much faster because there is no need to look for the cell in the XML data structure:

        $text = $table->get_cell("C5")->get_text;
        $text = $cells[1][1]->get_text;

Using such a mapping doesn't significanty improve the overall performances, but it allows the applications to execute the slow job once for all, then provide a good interactivity. However, be careful about very large areas: using get_cells() to load hundreds of thousands of cells may be practically too slow to be practical. In addition, the mapping is no longer accurate as soon as the structure of the underlying table is changed due to row/column insertions or deletions. For read-only access, have a look at the "read optimized" option (introduced below) that could help.

Working area limitation

The global size of a typical spreadsheet table is by far larger than the size of the really used part. As an example, your spreadsheet processor may silently store a 65536x1024 table while the last really used cell is, say, Z50, so the size of the useful part is 50x26. In such a situation, lpOD can't automatically decide what is the useful size, so it processes the full size. The first result is a huge time and resource waste. As soon as you know the useful size of a table, you can instruct the odf_table instance to ignore the extra area, thanks to set_working_area(). The instruction below tells that, for the current session, the table will be processed as if its size was 500x100:

        my $table = $doc->get_body->get_table("Sheet1");
        $table->set_working_area(500, 100);

Note that this operational restriction has no effect if the real size is smaller than the given size. On the other hand, set_working_area() doesn't destroy the table content that resides out of the working area, if any; it just prevents you from accessing any object beyond your declared limits through the official table-oriented methods, namely get_row(), get_cell(), and get_column(). However, the "hidden" area remains available for low-level hacking with basic element handling methods (for example, if you issue a get_paragraphs() from the table object, it will look for all the paragraphs belonging to all the real cells of the calling table).

The working area restriction doesn't produce any persistent effect when the document is saved.

Note that the get_size() method itself is affected by set_working_area(); it returns the declared size, unless the real size is smaller.

You can change the working area according to your current needs. Successive calls of set_working_area() are allowed, so the working area may be enlarged or reduced at will.

The working area restriction may be removed using set_working_area() without argument.

Read-only declaration

As soon as an object is selected using any official table component selector (such as get_cell(), get_row(), and so on), lpOD acts by default as if this object could be updated or deleted, and as if something (a row, a column or a cell) could be inserted before or after it. As a consequence, the internal data structure of the spreadsheet may be changed, resulting in useless processing if case of read-only access. However, lpOD allows the applications to use tables in "read optimized" mode, so it may avoid any update preparation, allowing better response times. To activate this mode, the user must set the "read optimized" flag to TRUE using read_optimize() like that:

        my $table = $doc->get_body->get_table("Sheet1");
        $table->read_optimize(TRUE);

Caution: read_optimize() means that you assume that you will not make updates; it doesn't prevent you from updating cells, deleting rows, and so on. So, be careful: you can corrupt the table and get very strange and unpredictable results as soon as you make updates in read optimized mode.

This optimization option is useful for large table area scans, particularly with very sparse tables (i.e. tables where significant cells are separated by large empty areas). On the other hand, it's not efficient, and at worst may increase the response time, for individual access to a cell. So don't use it without testing.

Note that you can switch this mode off and restore the default behavior at any time. You just have to recall read_optimize() with FALSE as argument. Like set_working_area(), read_optimize() doesn't produce any persistent effect.

However, there is a possible trap, illustrated by the next (wrong) example:

        $table->read_optimize(TRUE);
        $cell = $table->get_cell("Z26");
        $table->read_optimize(FALSE);
        $cell->set_value(1234);

In this sequence, we selected a cell while the table was in "read optimized" mode, then we cancelled this mode and executed an update. The result is not predictable (it will be sometimes right, sometimes wrong). The rule is: never update an object selected in read optimized mode. Before any update, we must select the object in normal mode.

COPYRIGHT & LICENSE

Copyright (c) 2010 Ars Aperta, Itaapy, Pierlis, Talend.

This work was sponsored by the Agence Nationale de la Recherche (http://www.agence-nationale-recherche.fr).

lpOD is free software; you can redistribute it and/or modify it under the terms of either:

a) the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. lpOD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with lpOD. If not, see http://www.gnu.org/licenses/.

b) the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0

cpanm ODF::lpOD

perl -MCPAN -e shell
install ODF::lpOD