If a is the array, I want a.index(a.max), but something more Ruby-like. It should be obvious, but I'm having trouble finding the answer at so and elsewhere. Obviously, I am new to Ruby.
Cary
views:
379answers:
3
+13
A:
For Ruby 1.8.7 or above:
a.each_with_index.max[1]
It does one iteration. Not entirely the most semantic thing ever, but if you find yourself doing this a lot, I would wrap it in an index_of_max method anyway.
Chuck
2010-01-27 20:02:11
Wow. How does this do what it does?
Wayne Conrad
2010-01-27 20:14:30
Agreed - how's this one work?
bergyman
2010-01-27 20:15:46
Aaah, got it. each_with_index.max returns an array with the first element being the value and the second being the index of it. Very nice, Chuck.
bergyman
2010-01-27 20:24:53
Although actually still foggy as to why exactly it returns an array like this...heh.
bergyman
2010-01-27 20:26:02
Chuck, I was aware of this method, but thought Ruby would have a way of returning just the index. (For any others new to Ruby, a.each_with_index.max returns the array [max value, index of max value], so Chuck is just pulling out the second element.)
Cary Swoveland
2010-01-27 20:32:52
`each_with_index` without a block returns an enumerator that gives the item and its index. We then send `max` to this enumerator, which does the standard `max` algorithm on item-index pairs. `Array.<=>` is implemented so that the first item determines the ordering (unless there's a tie, in which case the second is compared, and so on), so this works basically the same as doing `max` on an array of the values themselves. Then to get the index, we ask for the second item of the result (since we got a series of `[value, index]` pairs from `each_with_index`).
Chuck
2010-01-27 20:32:59
Boy, so is fast! The five comments before mine were posted while I was composing my comment.
Cary Swoveland
2010-01-27 20:34:37
Nice. I was unaware that doing a max on a 2D array like this just compares the value of the first element in each array.
bergyman
2010-01-27 20:37:58
That's a great way of doing it.If using Ruby 1.8.6, `require 'backports'` to get `#each_with_index`
Marc-André Lafortune
2010-01-27 21:07:29
A:
a = [1, 4 8]
a.inject(a[0]) {|max, item| item > max ? item : max }
At least it's Ruby-like :)
Jarrett Meyer
2010-01-27 20:02:45
A:
If you do an array.sort!, then the largest element will be the last one (array.last) and will have index array.length-1.
bta
2010-01-28 22:37:29
I expect there was no expressed support for your solution merely because sorting an array is an inefficient way of finding the max.
Cary Swoveland
2010-01-29 18:33:02
I agree, sorting an array just to find the max is inefficient. I mentioned it because I didn't know what else was being done with the array, so I thought I'd mention it in case the OP was going to sort it anyway for processing.
bta
2010-01-29 22:56:37