list sort requirements

SynapticBytes

Does the list.sort operator only work on single element lists? I tried it on a list of lists, and it doesn't seem to be having much luck in returning a meaningful sort?

jstrout

Sorting relies on ordering, i.e., it should have the same behavior as the ordering comparison operators (<, >, <=, and >=).

But no comparison is defined for lists or maps; those operators always return null on these. So, no, you can't meaningfully sort a list of lists. (Depending on your needs, you might be able to convert them to strings and sort those.)

SynapticBytes

OK. I was just looking for a quick way to sort the deck of cards in the playing card rosetta code, as a bonus round. Since they wanted a value for each card, I thought putting that in the first list element might have been an easy way to do it. No biggie.

jstrout

If it were me, I probably would store each card as a string in that case — "7H" for 7 of hearts, etc. Then you could sort them easily.

However, there is another sorting feature you may not know about, which is more intended for cases like this. list.sort takes an optional byKey parameter, which is a key to look up in each element, to sort by that. Example:

dogs = []
dogs.push {"name":"poodle", "size":2}
dogs.push {"name":"dachshund", "size":1}
dogs.push {"name":"collie", "size":3}
dogs.push {"name":"wolfhound", "size":4}

dogs.sort "name"
print "By name:" + dogs

dogs.sort "size"
print "By size:" + dogs

(Try it here.)

jstrout

Oh yeah, and though I illustrated it with a map key, it works with a list index too. So you could do what you originally wanted by simply using myList.sort 0, as shown here.