Last Friday of each month: Difference between revisions

for (classify *.month, Date.new("$year-01-01") .. Date.new("$year-12-31")).classify: *.month;

Here, <code>.classify</code> sorts the dates into one bin per month (but preserves the order in each bin). We then take the list inside each bin (<code>.value</code>) and find the last (<code>.reverse.first</code>) date which is a Friday.