NAME

TableData::Lookup - Lookup value in a table data structure

VERSION

This document describes version 0.001 of TableData::Lookup (from Perl distribution TableData-Lookup), released on 2021-01-16.

SYNOPSIS

 use TableData::Lookup qw(
     table_vlookup
 );

 # exact matching
 table_vlookup(
   table => [
     {min_income=>      0, tax_rate=>0.13},
     {min_income=>  8_000, tax_rate=>0.18},
     {min_income=> 15_000, tax_rate=>0.22},
     {min_income=> 35_000, tax_rate=>0.30},
     {min_income=> 85_000, tax_rate=>0.39},
     {min_income=>140_000, tax_rate=>0.45},
   ],
   lookup_field => 'min_income',
   lookup_value => 35_000,
   result_field => 'tax_rate',
 ); # => 0.30

 # exact matching, not found
 table_vlookup(
   table => [
     {min_income=>      0, tax_rate=>0.13},
     {min_income=>  8_000, tax_rate=>0.18},
     {min_income=> 15_000, tax_rate=>0.22},
     {min_income=> 35_000, tax_rate=>0.30},
     {min_income=> 85_000, tax_rate=>0.39},
     {min_income=>140_000, tax_rate=>0.45},
   ],
   lookup_field => 'min_income',
   lookup_value => 40_000,
   result_field => 'tax_rate',
 ); # => undef

 # approximate matching
 table_vlookup(
   table => [
     {min_income=>      0, tax_rate=>0.13},
     {min_income=>  8_000, tax_rate=>0.18},
     {min_income=> 15_000, tax_rate=>0.22},
     {min_income=> 35_000, tax_rate=>0.30},
     {min_income=> 85_000, tax_rate=>0.39},
     {min_income=>140_000, tax_rate=>0.45},
   ],
   lookup_field => 'min_income',
   lookup_value => 40_000,
   result_field => 'tax_rate',
   approx => 1,
 ); # => 0.30

 # approximate matching & interpolated result
 table_vlookup(
   table => [
     {min_income=>      0, tax_rate=>0.13},
     {min_income=>  8_000, tax_rate=>0.18},
     {min_income=> 15_000, tax_rate=>0.22},
     {min_income=> 35_000, tax_rate=>0.30},
     {min_income=> 85_000, tax_rate=>0.39},
     {min_income=>140_000, tax_rate=>0.45},
   ],
   lookup_field => 'min_income',
   lookup_value => 40_000,
   result_field => 'tax_rate',
   approx => 1,
   interpolate => 1,
 ); # => 0.309

FUNCTIONS

table_vlookup

Usage:

 table_vlookup(%args) -> any

Look up value in a table row by row.

This routine looks up value in a table row by row. It is similar to the spreadsheet function VLOOKUP, hence the same name being used. It is basically a glorified map()+grep() that returns a single value (or you can also say it's a glorified map+List::Util::first()).

Given a table, which is either an array-of-arrayrefs (aoa) or array-of-hashrefs (aoh), this routine will run through it row by row until it finds the value that you want. Once found, the value will be returned. Otherwise, undef is returned.

Exact matching

The table is expected to be sorted in ascending order by the lookup field. You specify a lookup value, which will be looked up in the lookup field. Once the value is found, the result field of the correspending row is returned and lookup is completed. When the lookup field already exceeds the lookup value, the routine also concludes that the value is not found, and the lookup is completed.

Example:

 table => [
   {min_income=>      0, tax_rate=>0.13},
   {min_income=>  8_000, tax_rate=>0.18},
   {min_income=> 15_000, tax_rate=>0.22},
   {min_income=> 35_000, tax_rate=>0.30},
   {min_income=> 85_000, tax_rate=>0.39},
   {min_income=>140_000, tax_rate=>0.45},
 ],
 lookup_field => 'min_income',
 lookup_value => 35_000,
 result_field => 'tax_rate',

will result in:

 0.30

while if the lookup_value is 40_000, undef will be returned since it is not found in any row of the table.

Approximate matching

If approx option is set to true, once the lookup field in a row exceeds the lookup value, the result field of the previous row will be returned (if any). For example, if lookup value is 40_000 then 0.30 will be returned (the row where min_income is 35_000) since the next row has min_income of 85_000 which already exceeds 40_000.

Interpolation of result

If, additionally, interpolate option is also set to true in addition to approx option being set to true, a linear interpolation will be done when an exact match fails. In the previous example, when lookup value is 40_000, 0.309 will be returned, which is calculated with:

 0.3 + (40_000 - 35_000)/(85_000 - 35_000)*(0.39 - 0.30)

In the case of there is no next row after min_income of 35_000, 0.30 will still be returned.

This function is not exported by default, but exportable.

Arguments ('*' denotes required arguments):

  • approx => bool

    Whether to do an approximate instead of an exact match.

    See example in the function description.

  • interpolate => bool

    Do a linear interpolation.

    When this option is set to true, will do a linear interpolation of result when an exact match is not found. This will only be performed if approx is also set to true.

    See example in the function description.

    Currently, you cannot use interpolate with lookup_code.

  • lookup_code => code

    Supply code to match a row.

    Unless what you want to match is custom, you usually specify lookup_value and lookup_field instead.

    The code will be passed the row (which is an arrayref or a hashref) and optionally the lookup value too as the second argument if the lookup value is specified. It is expected to return either -1, 0, 1 like the Perl's cmp or <=> operator. -1 means the lookup field is less than the lookup value, 0 means equal, and 1 means greater than.

    With approx option not set to true, lookup will succeed once 0 is returned. With approx set to true, lookup will succeed once 0 or 1 is returned.

  • lookup_field => str

    Where to look up the lookup value in.

    Either an integer array index (for aoa table) or a string hash key (for aoh table).

    Instead of lookup_value and lookup_field, you can also specify lookup_code instead.

  • lookup_value => any

    The value that you want to look up in the lookup field.

    Instead of lookup_value and lookup_field, you can also specify lookup_code instead.

  • result_field* => str

    Where to get the result from.

    Either an integer array index (for aoa table) or a string hash key (for aoh table).

  • table* => array

Return value: (any)

HOMEPAGE

Please visit the project's homepage at https://metacpan.org/release/TableData-Lookup.

SOURCE

Source repository is at https://github.com/perlancar/perl-TableData-Lookup.

BUGS

Please report any bugs or feature requests on the bugtracker website https://github.com/perlancar/perl-TableData-Lookup/issues

When submitting a bug or request, please include a test-file or a patch to an existing test-file that illustrates the bug or desired feature.

SEE ALSO

AUTHOR

perlancar <perlancar@cpan.org>

COPYRIGHT AND LICENSE

This software is copyright (c) 2021 by perlancar@cpan.org.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.