Stem-and-leaf plot

Handles negative stems properly.

my @data = <
     12 127  28  42  39 113  42  18  44 118  44
     37 113 124  37  48 127  36  29  31 125 139
    131 115 105 132 104 123  35 113 122  42 117
    119  58 109  23 105  63  27  44 105  99  41
    128 121 116 125  32  61  37 127  29 113 121
     58 114 126  53 114  96  25 109   7  31 141
     46  13  27  43 117 116  27   7  68  40  31
    115 124  42 128  52  71 118 117  38  27 106
     33 117 116 111  40 119  47 105  57 122 109
    124 115  43 120  43  27  27  18  28  48 125
    107 114  34 133  45 120  30 127  31 116 146
>».Int.sort;
 
my Int $stem_unit = 10;
my %h = @data.classify: * div $stem_unit;
 
my $range = [minmax] %h.keys».Int;
my $stem_format =  "%{$range.min.chars max $range.max.chars}d";
 
for $range.list -> $stem {
    my $leafs = %h{$stem} // [];
    say $stem.fmt($stem_format), ' | ', ~$leafs.map: * % $stem_unit;
}

Output:

 0 | 7 7
 1 | 2 3 8 8
 2 | 3 5 7 7 7 7 7 7 8 8 9 9
 3 | 0 1 1 1 1 2 3 4 5 6 7 7 7 8 9
 4 | 0 0 1 2 2 2 2 3 3 3 4 4 4 5 6 7 8 8
 5 | 2 3 7 8 8
 6 | 1 3 8
 7 | 1
 8 | 
 9 | 6 9
10 | 4 5 5 5 5 6 7 9 9 9
11 | 1 3 3 3 3 4 4 4 5 5 5 6 6 6 6 7 7 7 7 8 8 9 9
12 | 0 0 1 1 2 2 3 4 4 4 5 5 5 6 7 7 7 7 8 8
13 | 1 2 3 9
14 | 1 6