Good afternoon!

I'm a researcher in the Humanities and I'm trying my hand at a bit of programming to aid in the analysis of a large dataset. I've got as far as storing my data in a hash of hashes. They keys are the pseudonyms of my participants and the values are the dates (in YYYYMM format) that they attended my programme, and then I also have how many times they attended each month (but this isn't relevant to my question today). What I want to do is, for each participant, print out the earliest and latest date that they attended.

I found some code on StackExchange (reproduced below) which worked okay for the example given on that site, but I think I have misunderstood something because it doesn't produce the expected output using an extract from my dataset. Included below is the code I'm using, the actual output, and the expect output. I would be very grateful for any pointers about what I've done wrong here. Thanks very much in advance. 

 my %counts = (
     "Adam"      => { "201708"   => 1, "201703" => 1, "201804" => 1, "
+201603" => 1, "201705" => 1, "201702" => 1, "201608" => 1, "201704" =
+> 1,},
     "Sam" => { "201803"  => 1,  "201801" => 1 },
 );

use List::UtilsBy 'max_by';
foreach my $key ( keys %counts ) {
    my $subhash = $counts{$key};
    my $maximal = max_by { $subhash->{$_} } keys %$subhash;
    print "$key, $maximal\n";
}


use List::UtilsBy 'min_by';
foreach my $key ( keys %counts ) {
    my $subhash = $counts{$key};
    my $minimal = max_by { $subhash->{$_} } keys %$subhash;
    print "$key, $minimal\n";
}

[download]
------------
OUTPUT
Adam, 201704
Sam, 201801
Adam, 201704
Sam, 201801
-------------

EXPECTED OUTPUT
Adam, 201804
Sam, 201803
Adam, 201603
Sam, 201801

[download]

In reply to Using List::UtilsBy to print max and min values from a hash of hashes by Izzy_Murph

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