How to grep undefined values in an array?

Question

I have an array with an undefined value:

[0] 0.1431,
[1] undef

I then later push this value onto an array, and Perl doesn't warn me about the uninitialized values (I cannot imagine why someone would want this to happen without a warning or die, even when I have use autodie ':all' set, but that's another story)

So I try and grep on these arrays to prevent pushing undef values onto arrays, thus:

if (grep {undef} @array) {
    next
}

But, this doesn't catch the value.

How can I grep for undefined values in Perl5?

Re "But, this doesn't catch the value.", undef doesn't check if something is undefined; it makes things undefined and/or returns an undefined scalar (depending on how it's used) — ikegami
– ikegami, Commented Nov 5, 2020 at 19:15
Re "even when I have use autodie ':all' set", push can't fail, so the concept of making it die on failure makes no sense. — ikegami
– ikegami, Commented Nov 5, 2020 at 19:20

stevieb · Accepted Answer · 2020-11-05 19:00:47Z

5

grep for not defined instead:

use warnings;
use strict;

my @array = (0, undef, undef, 3);

if (grep {! defined} @array) {
    print "undefined values in array\n";
}

There are several reasons as to why you'd want to have/allow undefined values in an array. One such beneficial scenario is when passing in positional parameters to a function.

answered Nov 5, 2020 at 19:00

stevieb

9,3263 gold badges28 silver badges39 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

ikegami · Accepted Answer · 2020-11-05 19:22:28Z

3

Why not prevent the values from being added in the first place?

Replace

push @array, LIST;

with

push @array, grep defined, LIST;

If it's specifically a scalar, you could also use

push @array, $scalar if defined($scalar);

answered Nov 5, 2020 at 19:22

ikegami

391k17 gold badges291 silver badges555 bronze badges

Comments

toolic · Accepted Answer · 2020-11-05 19:15:27Z

2

You can use defined to get rid of undefined items:

use warnings;
use strict;
use Data::Dumper;

my @a1 = (1,2,3,undef,undef,4);
print Dumper(\@a1);

my @a2 = grep { defined } @a1;
print Dumper(\@a2);

Output:

edited Nov 5, 2020 at 19:15

answered Nov 5, 2020 at 19:00

toolic

62.9k21 gold badges81 silver badges130 bronze badges

Collectives™ on Stack Overflow

How to grep undefined values in an array?

3 Answers 3

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related