How can I find the indexes of an element in Haskell list

Question

Here is a Haskell list:

[[1],[3,5],[],[1,9],[3,5],[9,7],[1,9]]

I want to find the exact index of its elements. I tried to use elemIndex but it doesn't give the correct index when I try to find duplicated element like [3,5] and [1,9].

when you look for a duplicated element, do you want the first index, the last index, or all indices? — genisage
– genisage, Commented Dec 16, 2014 at 22:10
Do you mean you want to find all the locations of [3,5] - not jus the first? — ErikR
– ErikR, Commented Dec 16, 2014 at 22:10
Yes! all locations. For example for [3,5] the index will be [1,4] — Myke
– Myke, Commented Dec 16, 2014 at 22:12

jamshidh · Accepted Answer · 2014-12-16 22:12:00Z

1

Is this what you want?

> elemIndices  [3,5] [[1],[3,5],[],[1,9],[3,5],[9,7],[1,9]]
[1,4]

answered Dec 16, 2014 at 22:12

jamshidh

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1 Comment

Myke Over a year ago

How about if I want to associate it with it's index like [(0,[1]), (1,[3,5]), (2,[]), (3,[1,9]), (4,[3,5]), (5,[9,7]), (6,[1,9])]

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