如何在J中将相等值分组？

Question

   (= <@#"1 0 ~.) 3 2 3 3 4
+-----+-+-+
|3 3 3|2|4|
+-----+-+-+

What other ways are there? I mostly don't like the part where it says "1 0 .

Answer 1

The adverb key ( /. ) groups the right argument as specified by the left argument and applies a verb to each group. If you give it the same left and right argument you can apply the verb box ( < ) to group all the equal items

   </.~ 3 2 3 3 4
┌─────┬─┬─┐
│3 3 3│2│4│
└─────┴─┴─┘

You could easily sum the groups instead:

   +//.~ 3 2 3 3 4
9 2 4