CODEWITHSUNDEEP
perl
con
con

Reputation: 6123

How to do `defined` with a hash slice

I'm trying to learn Perl better, and learn hash slices.

Instead of 3 different if (defined statements, I'm trying to tidy the code to make it more maintainable and readable, but have come across the following conundrum:

#!/usr/bin/env perl

use strict;
use warnings FATAL => 'all';
use feature 'say';
use autodie ':all';
use Carp 'confess';
use DDP; # a.k.a. Data::Printer
use JSON 'decode_json';

my $hashref;
$hashref->{Jane} = decode_json('{"sex":"Female","Mortality_Status":"Alive", "latest_date":"2020-11-26","Hospitalized":"no","Risk_Status":"NA"}');
p $hashref; # pretty print the data
my @needed_terms = qw(age BMI sex);
if (defined @{ $hashref->{Jane} }{@needed_terms}) {
    say 'all terms are defined.'; # this is what it says, which is WRONG!!!
} else {
    say 'some terms are missing.'; # Jane is missing BMI and age, so the script should print here
}

I've read How to do sum of hash reference slice? and https://perlmonks.org/?node=References+quick+reference to no avail.

This person Jane is missing both age and BMI information, so the if (defined statement should say that some terms are missing, but is instead passing.

I get the same error whether I use @{ $hashref->{Jane} }{@needed_terms} or %{ $hashref->{Jane} }{@needed_terms}

I've also thought that maybe defined is returning how many terms of the slice are defined, but that isn't true.

How can I set if (defined statement on a hash slice properly?

Upvotes: 4

Views: 111

Answers (1)

toolic
toolic

Reputation: 62227

This is a good place to use all from List::Util:

use List::Util qw(all);

if (all { exists $hashref->{Jane}{$_} } @needed_terms) {
    say 'all terms are defined.';
} else {
    say 'some terms are missing.'; # Jane is missing BMI and age, so the script should print here
}

It loops through all the needed terms and checks to see if each exists as key to the Jane hash.

One of my favorite docs for Perl Data Structures is perldoc perldsc. It is more of a step-by-step tutorial than References quick reference.

Upvotes: 3

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