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Manual Reference Pages  -  TEXT::CSV::HASHIFY (3)

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Text::CSV::Hashify - Turn a CSV file into a Perl hash



    # Simple functional interface
    use Text::CSV::Hashify;
    $hash_ref = hashify(/path/to/file.csv, primary_key);

    # Object-oriented interface
    use Text::CSV::Hashify;
    $obj = Text::CSV::Hashify->new( {
        file        => /path/to/file.csv,
        format      => hoh, # hash of hashes, which is default
        key         => id,  # needed except when format is aoh
        max_rows    => 20,    # number of records to read; defaults to all
        ... # other key-value pairs possible for Text::CSV
    } );

    # all records requested
    $hash_ref       = $obj->all;

    # arrayref of fields input
    $fields_ref     = $obj->fields;

    # hashref of specified record
    $record_ref     = $obj->record(value_of_key);

    # value of one field in one record
    $datum          = $obj->datum(value_of_key, field);

    # arrayref of all unique keys seen
    $keys_ref       = $obj->keys;


The Comma-Separated-Value (’CSV’) format is the most common way to store spreadsheets or the output of relational database queries in plain-text format. However, since commas (or other designated field-separator characters) may be embedded within data entries, the parsing of delimited records is non-trivial. Fortunately, in Perl this parsing is well handled by CPAN distribution Text::CSV. This permits us to address more specific data manipulation problems by building modules on top of Text::CSV.

<B>Note:B> In this document we will use CSV as a catch-all for tab-delimited files, pipe-delimited files, and so forth. Please refer to the documentation for Text::CSV to learn how to handle field separator characters other than the comma.

    Primary Case: CSV (with primary key) to Hash of Hashes

Text::CSV::Hashify is designed for the case where you simply want to turn a CSV file into a Perl hash. In particular, it is designed for the case where (a) the CSV file’s first record is a list of fields in the ancestral database table and (b) one field (column) functions as a <B>primary keyB>, i.e., each record’s entry in that field is non-null and is distinct from every other record’s entry therein.

Text::CSV::Hashify turns that kind of CSV file into one big hash of hashes. Elements of this hash are keyed on the entries in the designated primary key field and the value for each element is a hash reference of all the data in a particular database record (including the primary key field and its value).

    Secondary Case: CSV (lacking primary key) to Array of Hashes

You may, however, encounter cases where a CSV file’s header row contains the list of database fields but no field is capable of serving as a primary key, i.e., there is no field in which the entry for that field in any record is guaranteed to be distinct from the entries in that field for all other records.

In this case, while an individual record can be turned into a hash, the CSV file as a whole cannot accurately be turned into a hash of hashes. As a fallback, Text::CSV::Hashify can, upon request, turn this into an array of hashes. In this case, you will not be able to look up a particular record by its primary key. You will instead have to know its index position within the array (which is equivalent to knowing its record number in the original CSV file minus 1).


Text::CSV::Hashify provides two interfaces: one functional, one object-oriented.

Use the functional interface when all you want is to turn a CSV file with a primary key field into a hash of hashes.

Use the object-oriented interface for any more sophisticated manipulation of the CSV file. This includes:
o Text::CSV options

Access to any of the options available to Text::CSV, such as use of a separator character other than a comma.

o Limit number of records

Selection of a limited number of records from the CSV file, rather than slurping the whole file into your in-memory hash.

o Array of hash references format

Probably better than the default hash of hash references format when the CSV file has no field able to serve as a primary key.

o Metadata

Access to the list of fields, the list of all primary key values, the values in an individual record, or the value of an individual field in an individual record.

<B>Note:B> On the recommendation of the authors/maintainers of Text::CSV, Text::CSV::Hashify will internally always set Text::CSV’s binary => 1 option.


Text::CSV::Hashify by default exports one function: hashify().

    $hash_ref = hashify(/path/to/file.csv, primary_key);

Function takes two arguments: path to CSV file; field in that file which serves as primary key.

Returns a reference to a hash of hash references.



o Purpose

Text::CSV::Hashify constructor.

o Arguments

    $obj = Text::CSV::Hashify->new( {
        file        => /path/to/file.csv,
        format      => hoh, # hash of hashes, which is default
        key         => id,  # needed except when format is aoh
        max_rows    => 20,    # number of records to read; defaults to all
        ... # other key-value pairs possible for Text::CSV
    } );

Single hash reference. Required element is:
o file

String: path to CSV file serving as input.

Element usually needed:
o key

String: name of field in CSV file serving as unique key. Needed except when optional element format is aoh.

Optional elements are:
o format

String: possible values are hoh and aoh. Defaults to hoh (hash of hashes). new() will fail if the same value is encountered in more than one record’s entry in the key column. So if you know in advance that your data cannot meet this condition, explicitly select format => aoh.

o max_rows

Number: provide this if you do not wish to populate the hash with all data records from the CSV file. (Will have no effect if the number provided is greater than or equal to the number of data records in the CSV file.)

o Any option available to Text::CSV

See documentation for either Text::CSV or Text::CSV_XS.

o Return Value

Text::CSV::Hashify object.

o Comment


o Purpose

Get a representation of all data found in a CSV input file.

o Arguments

    $hash_ref   = $obj->all; # when format is default or hoh
    $array_ref  = $obj->all; # when format is aoh

o Return Value

Reference representing all data records in the CSV input file. In the default case, or if you have specifically requested format = ’hoh’>, the return value is a hash reference. When you have requested format = ’aoh’>, the return value is an array reference.

o Comment

In the default (hoh) case, the return value is equivalent to that of hashify().


o Purpose

Get a list of the fields in the CSV source.

o Arguments

    $fields_ref = $obj->fields;

o Return Value

Array reference.

o Comment

If any field names are duplicate, you will not get this far, as new() would have died.


o Purpose

Get a hash representing one record in the CSV input file.

o Arguments

    $record_ref = $obj->record(value_of_key);

One argument. In the default case (format => hoh), this argument is the value in the record in the column serving as unique key.

In the format => aoh case, this will be index position of the data record in the array. (The header row will be at index 0.)

o Return Value

Hash reference.


o Purpose

Get value of one field in one record.

o Arguments

    $datum = $obj->datum(value_of_key, field);

List of two arguments: the value in the record in the column serving as unique key; the name of the field.

o Return Value



o Purpose

Get a list of all unique keys found in the input file.

o Arguments

    $keys_ref = $obj->keys;

o Return Value

Array reference.

o Comment

If you have selected format => aoh in the options to new(), the keys method is inappropriate and will cause your program to die.


    James E Keenan
    CPAN ID: jkeenan


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

The full text of the license can be found in the LICENSE file included with this module.

Copyright 2012-15, James E Keenan. All rights reserved.


Thanks to Christine Shieh for serving as the alpha consumer of this library’s output.


    Text-CSV and Text-CSV_XS

These distributions underlie Text-CSV-Hashify and provide all of its file-parsing functionality. Where possible, install both. That will enable you to process a file with a single, shared interface but have access to the faster processing speeds of XS where available.


Like Text-CSV-Hashify, Text-CSV-Slurp slurps an entire CSV file into memory, but stores it as an array of hashes instead.


This distribution inspired the max_rows option to new().
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perl v5.20.3 TEXT::CSV::HASHIFY (3) 2015-06-06

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