Perl: How to simultaneously access mutliple nonconsecutive elements in an array?

Question

The array I want to query does not change during execution:

my @const_arr=qw( a b c d e f g);

The input is a string containing the indices I want to access, for example:

my $str ="1,4";

Is there something (besides iterating over the indices in $str) along the lines of @subarray = @const_arr[$str] that will result in @subarray containing [b,e] ?

And to answer my own question.. @subarray=@const_arr[eval($str)] — Noam Kremen
– Noam Kremen, Commented Jan 23, 2012 at 16:52
Using eval to parse your input is overkill, and opens the door to security issues. split is a better tool for the job. — Eric Strom
– Eric Strom, Commented Jan 23, 2012 at 17:17

choroba · Accepted Answer · 2012-01-23 17:10:46Z

5

If the indices are in a string, you can split the string to get them:

@array    = qw(a b c d e);
$indices  = '1,4';
@subarray = @array[split /,/, $indices];
print "@subarray\n";

answered Jan 23, 2012 at 17:10

choroba

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3 Comments

zgpmax Over a year ago

This answer would be better if it kept the 'my's and variable names from the question.

choroba Over a year ago

@hochgurgler: Well, I cannot use the name "const" for something that is not a constant :-)

ikegami Over a year ago

@choroba, One could argue that using the name "@const_arr" makes it a constant. (Just not one enforced by the compiler.)

JRFerguson · Accepted Answer · 2012-01-23 16:56:37Z

4

An array slice will do this:

@const_arr=qw(a b c d e);
@subarray=(@const_arr)[1,4];
print "@subarray"'

answered Jan 23, 2012 at 16:56

JRFerguson

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1 Comment

zgpmax Over a year ago

This answer doesn't address the issue of how to get from the string "1,4" to the list (1,4)

Eric Strom · Accepted Answer · 2012-01-23 17:11:02Z

4

my @const_arr = qw(a b c d e f);  # the {...} creates a hash reference, 
                                  # not what you wanted

my $str = "1,4";

my @idx = split /,/ => $str;

my @wanted = @const_arr[@idx];

or in one line:

my @wanted = @const_arr[split /,/ => $str];

answered Jan 23, 2012 at 17:11

Eric Strom

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Comments

Taras · Accepted Answer · 2012-01-23 16:55:49Z

3

@const_arr should initiate like this:

my @const_arr = qw(a b c d e f);

then you can access to 1 and 4 element by:

@const_arr[1,4]

answered Jan 23, 2012 at 16:55

Taras

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