Index of element in array F#

Question

Good day.

How to find index of the element in array? No word about it in docs. Only way I found is:

let arr = [|1; 4; 5; 10|]
let elem = 5
let i = Array.findIndex (fun e -> e = elem) arr

seems to me you answered your own question already - so what is the question? — Random Dev
– Random Dev, Commented Jan 25, 2016 at 5:48
I thought my method is a kludge and there is more elegant one. — Feofilakt
– Feofilakt, Commented Jan 25, 2016 at 5:53
you could reduce the lambda to ((=) elem) and there is Array.IndexOf but basically those are just a matter of taste — Random Dev
– Random Dev, Commented Jan 25, 2016 at 6:05
Also consider tryFindIndex for those cases where you aren't 100 % sure that the element is in the array. — Mark Seemann
– Mark Seemann, Commented Jan 25, 2016 at 6:34
When you say 'kludge', do you mean 'inefficient' or do you mean 'ugly code'. If you mean 'inefficient', then consider using Map with your elements as the key and index as the value, thus providing fast lookup of the index value [O(log N)]. — James Hugard
– James Hugard, Commented Jan 26, 2016 at 5:59

Sedat Kapanoglu · Accepted Answer · 2016-01-25 07:36:21Z

5

You can create a shortcut function yourself if you use it frequently:

let findIndex arr elem = arr |> Array.findIndex ((=) elem)
...
let i = findIndex arr elem

answered Jan 25, 2016 at 5:58

Sedat Kapanoglu

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2 Comments

Or: let findIndex arr elem = arr |> Array.findIndex ((=) elem)

@Foole much more elegant. I'll incorporate it.