Last time, a time long, long ago, in a universe far, far away, I left you with the following Perl 6 code (or something like it). This code reads in a series of book heights and displays the number of books of each height (in order from shortest to tallest).

my %num_of_height;
for lines() {
    if m/^ \s* (\d+[\.\d+]?) [\s* x \s* (\d+)]? \s* $/ {
        my $height = +$0;
        my $num = +($1 || 1);
        %num_of_height{$height} += $num;
    } elsif ! m/^\s*$/ {
        note "Invalid line ignored: $_";
    }
}

#| unique book heights seen, in order from shortest to tallest
my @heights = sort { $^a <=> $^b }, keys %num_of_height;

say "Histogram data:";
for @heights -> $height {
    my $num = %num_of_height{$height};
    say "$height x $num";
}

As you may recall, this little bit of somewhat less-than-useful P6 script was inspired by a homework assignment in my daughter’s high-school statistics course. While she manually counted up the heights of the books we measured, in order to draw a histogram of the data, I wrote a Perl script to do the same counting.

Since then, for kicks, I’ve also hacked together about 50 lines of code to display an actual histogram of these data, with horizontal bars of *****. I’m not going to go into that code here, because I did not write it at the time, but if you want, you can check it out on Github.

However, I did discover how succinctly Perl 6 could answer the other questions from the assignment.

When my daughter told me she was taking statistics, I wondered how she could do that without knowing any calculus. Then on second thought, I guess there is a certain amount you can do with statistics, even without knowing any calculus.

Ah, yes. And last night’s homework assignment drilled that home. She asked me to help her. First, she needed to find a quantitative data set she could use to construct a histogram. Looking around the living room, I suggested, “What about the heights of the books on my book shelves? You could measure the spines and write them down in a data table.”

Now, I currently have nine full shelves of books in my living room, everything from Dave Barry and Dilbert to Peopleware to marketing and memoirs, theology and psychology, short stories and the theory of writing, to Holly Lisle, Douglas Adams, Robert Heinlein, and The Sisterhood of the Traveling Pants. (And I am not making this up.) And those are just the books that are actually on shelves, not the books that are still in boxes.

I think she was a little overwhelmed by the idea.

“You don’t have to include all the books, just one or two shelves worth. Maybe that one over there, half full of mass-market paperbacks all the same size.” Easy to measure, easy to count.

So we chose that shelf and the shelf just under it, a nice cross-section of fiction in mass-market, trade paperback, and hardcover. And then while she was manually collating the data, inspiration struck me. Why don’t I write a quick Perl 6 script to check her results. It’ll give me something to write about; plus I’ll see whether Perl 6 is really useful for anything, especially minor scripts.

And as it turns out, it might be.