If there's always just one id_2 per id_1, you can use 
my %hash = map +($_->{id_1} => { $_->{id_2} => $_->{v} }), @aoh;

[download]

Otherwise, you need to assign to the inner hash not to overwrite a previous branch.

Tried with 

my @aoh = (
            { id_1 => "F1", id_2 => "F2", v => "FV" },
            { id_1 => "S1", id_2 => "S2", v => "SV" },
            { id_1 => "T1", id_2 => "T2", v => "TV" },
            { id_1 => "T1", id_2 => "T3", v => "TW" },
          );

[download]

Another approach would be to use Data::Diver: 

use Data::Diver qw{ DiveVal };

my %hash;
DiveVal(\%hash, @$_{qw{ id_1 id_2 }}) = $_->{v} for @aoh;

[download]

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,

[download]

In reply to Re: map into a multidimensional hash by choroba
in thread map into a multidimensional hash by nikmit

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