# Finding Position of Element in an Array
**URL:** https://discourse.julialang.org/t/finding-position-of-element-in-an-array/12502
**Category:** General Usage
**Tags:** question
**Created:** [July 19, 2018, 4:25pm UTC](https://discourse.julialang.org/t/finding-position-of-element-in-an-array/12502 "2018-07-19T16:25:22Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@jazzieman](https://discourse.julialang.org/u/jazzieman)
#### Post date: [July 19, 2018, 4:25pm UTC](https://discourse.julialang.org/t/finding-position-of-element-in-an-array/12502/1 "2018-07-19T16:25:22Z")
I’m looking for a function (is there is one) where i can get the position of an element in an array? I have a 3D array of numbers and i want to obtain the position (i,j,k)of a particular number (element) in that array. Is there a way to obtain it? Thanks in advance.
---
### Author:  [@dpsanders](https://discourse.julialang.org/u/dpsanders)
#### Post date: [July 19, 2018, 4:26pm UTC](https://discourse.julialang.org/t/finding-position-of-element-in-an-array/12502/2 "2018-07-19T16:26:32Z")
The following works on Julia 0.6:
```julia
julia> A = rand(1:3, 3, 3, 3)
3×3×3 Array{Int64,3}:
[:, :, 1] =
2 3 2
2 2 2
2 1 3
[:, :, 2] =
3 3 3
2 1 3
3 1 1
[:, :, 3] =
3 2 1
2 2 2
3 1 1
julia> findall(x->x==2, A)
11-element Array{CartesianIndex{3},1}:
CartesianIndex(1, 1, 1)
CartesianIndex(2, 1, 1)
CartesianIndex(3, 1, 1)
CartesianIndex(2, 2, 1)
CartesianIndex(1, 3, 1)
CartesianIndex(2, 3, 1)
CartesianIndex(2, 1, 2)
CartesianIndex(2, 1, 3)
CartesianIndex(1, 2, 3)
CartesianIndex(2, 2, 3)
CartesianIndex(2, 3, 3)
```
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### Author:  [@jazzieman](https://discourse.julialang.org/u/jazzieman)
#### Post date: [July 19, 2018, 5:22pm UTC](https://discourse.julialang.org/t/finding-position-of-element-in-an-array/12502/3 "2018-07-19T17:22:18Z")
> [@dpsanders](#):
>
> findall(x-\>x==2, A)
Thank you for the prompt response. I tried it but i get the following error:
_findall(x-\>x==2, A)_
_ERROR: UndefVarError: findall not defined_
Apratently i dont have that function. When i look the function it tells me:
Binding findall does not exis
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### Author:  [@DNF](https://discourse.julialang.org/u/DNF)
#### Post date: [July 19, 2018, 5:45pm UTC](https://discourse.julialang.org/t/finding-position-of-element-in-an-array/12502/4 "2018-07-19T17:45:19Z")
`findall` is the name in version 0.7. In version 0.6 you just use `find` instead.
---
### Author:  [@jazzieman](https://discourse.julialang.org/u/jazzieman)
#### Post date: [July 19, 2018, 6:01pm UTC](https://discourse.julialang.org/t/finding-position-of-element-in-an-array/12502/5 "2018-07-19T18:01:45Z")
> [@dpsanders](#):
>
> findall(x-\>x==2, A)
I used find and i get the following:
find(x-\>x==2, A)
10-element Array{Int64,1}:
1
5
10
11
12
14
17
19
26
27
What i need is the position (CartesianIndex). What am I doing wrong?
---
### Author:  [@abobroff](https://discourse.julialang.org/u/abobroff)
#### Post date: [July 20, 2018, 5:39am UTC](https://discourse.julialang.org/t/finding-position-of-element-in-an-array/12502/6 "2018-07-20T05:39:54Z")
> …i want to obtain the position (i,j,k)of a particular number (element) in that array.
`ind2sub(A, find(A .== 2))`
EDIT (for v0.6)
```julia
i, j, k = ind2sub(A, find(x->x == 2,A))
idx = [i j k]
```
---
### Author:  [@RoyiAvital](https://discourse.julialang.org/u/RoyiAvital)
#### Post date: [July 20, 2018, 6:31am UTC](https://discourse.julialang.org/t/finding-position-of-element-in-an-array/12502/7 "2018-07-20T06:31:41Z")
Is there a mode for `findall()` in 0.7 which works with linear indices?
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### Author:  [@DNF](https://discourse.julialang.org/u/DNF)
#### Post date: [July 20, 2018, 7:38am UTC](https://discourse.julialang.org/t/finding-position-of-element-in-an-array/12502/8 "2018-07-20T07:38:47Z")
> [@abobroff](#):
>
> `ind2sub(A, find(A .== 2))`
It is normally preferable to use `find(x->x==2, A)` over `find(A.==2)`.
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### Author:  [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)
#### Post date: [July 20, 2018, 8:30am UTC](https://discourse.julialang.org/t/finding-position-of-element-in-an-array/12502/9 "2018-07-20T08:30:18Z")
You can convert, something like
```julia
julia> v = rand(3,3);
julia> C = findall(x->x>0.5, v)
5-element Array{CartesianIndex{2},1}:
CartesianIndex(2, 1)
CartesianIndex(2, 2)
CartesianIndex(3, 2)
CartesianIndex(2, 3)
CartesianIndex(3, 3)
julia> L = LinearIndices(v)
3×3 LinearIndices{2,Tuple{Base.OneTo{Int64},Base.OneTo{Int64}}}:
1 4 7
2 5 8
3 6 9
julia> L[C]
5-element Array{Int64,1}:
2
5
6
8
9
```
---
### Author:  [@abobroff](https://discourse.julialang.org/u/abobroff)
#### Post date: [July 20, 2018, 10:02am UTC](https://discourse.julialang.org/t/finding-position-of-element-in-an-array/12502/10 "2018-07-20T10:02:43Z")
> [@RoyiAvital](#):
>
> Is there a mode for `findall()` in 0.7 which works with linear indices?
As wrote Kristoffer:
`(LinearIndices(A))[findall(x->x == 2, A)]`
---
### Author:  [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)
#### Post date: [July 20, 2018, 10:34am UTC](https://discourse.julialang.org/t/finding-position-of-element-in-an-array/12502/11 "2018-07-20T10:34:12Z")
You can also do
```julia
julia> C = findall(x->x>0.5, vec(v))
3-element Array{Int64,1}:
1
2
4
```
---
### Author:  [@RoyiAvital](https://discourse.julialang.org/u/RoyiAvital)
#### Post date: [July 20, 2018, 10:35am UTC](https://discourse.julialang.org/t/finding-position-of-element-in-an-array/12502/12 "2018-07-20T10:35:16Z")
Is it efficient?
Could we not add mode for `findall()` to iterate to through all elements in one loop?
Does Julia have more efficient way to work on the array (Like looping on its length)?
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### Author:  [@abobroff](https://discourse.julialang.org/u/abobroff)
#### Post date: [July 20, 2018, 11:03am UTC](https://discourse.julialang.org/t/finding-position-of-element-in-an-array/12502/13 "2018-07-20T11:03:36Z")
I think Kristoffer solved this problem:
> [@kristoffer.carlsson](#):
>
> C = findall(x-\>x\>0.5, vec(v))
---
### Author:  [@jazzieman](https://discourse.julialang.org/u/jazzieman)
#### Post date: [July 20, 2018, 3:48pm UTC](https://discourse.julialang.org/t/finding-position-of-element-in-an-array/12502/14 "2018-07-20T15:48:12Z")
Thanks to you all. Since I don,'t have findall, I tried `ind2sub(A, find(A == 2))` and it worked!!
---
### Author:  [@RoyiAvital](https://discourse.julialang.org/u/RoyiAvital)
#### Post date: [July 20, 2018, 4:49pm UTC](https://discourse.julialang.org/t/finding-position-of-element-in-an-array/12502/15 "2018-07-20T16:49:52Z")
> [@abobroff](#):
>
> I think Kristoffer solved this problem:
>
> > [@kristoffer.carlsson](#):
> >
> > C = findall(x-\>x\>0.5, vec(v))
How does it compare to something like:
`y = [i for i ∈ 1:length(x) if x[i] > 0.5];`
---
### Author:  [@dpsanders](https://discourse.julialang.org/u/dpsanders)
#### Post date: [July 20, 2018, 5:32pm UTC](https://discourse.julialang.org/t/finding-position-of-element-in-an-array/12502/16 "2018-07-20T17:32:15Z")
Try it and see?
[Put both in functions and use `BenchmarkTools.jl`.]
---
### Author:  [@lmiq](https://discourse.julialang.org/u/lmiq)
#### Post date: [February 4, 2019, 4:51pm UTC](https://discourse.julialang.org/t/finding-position-of-element-in-an-array/12502/17 "2019-02-04T16:51:30Z")
It seems that “find” is not available anymore in Julia 1.0, correct?
If so, how do I find the index of an element in a vector?
Such as: a = [“a”, “b”, “c”, “d”]
find “3” for the index of element “c”.
Thank you. (if there is any particularly efficient intrinsic function to do so, of course).
---
### Author:  [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)
#### Post date: [February 4, 2019, 5:01pm UTC](https://discourse.julialang.org/t/finding-position-of-element-in-an-array/12502/18 "2019-02-04T17:01:05Z")
`findfirst` or `findall`, both of which are well-documented with examples
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### Author:  [@lmiq](https://discourse.julialang.org/u/lmiq)
#### Post date: [February 4, 2019, 5:13pm UTC](https://discourse.julialang.org/t/finding-position-of-element-in-an-array/12502/19 "2019-02-04T17:13:08Z")
I tried to use findfirst, but it seems that it only works for string inputs, not vector inputs.
```julia
julia> a = ["a", "b", "c", "d"]
4-element Array{String,1}:
"a"
"b"
"c"
"d"
julia> findfirst("c",a)
ERROR: MethodError: no method matching findfirst(::String, ::Array{String,1})
```
---
### Author:  [@nilshg](https://discourse.julialang.org/u/nilshg)
#### Post date: [February 4, 2019, 5:20pm UTC](https://discourse.julialang.org/t/finding-position-of-element-in-an-array/12502/20 "2019-02-04T17:20:25Z")
Maybe `findfirst((x -> x=="c"), a)`? (Slightly contrived, there might be a better way?)
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