# Changing content of an array via a function

**URL:** <https://discourse.julialang.org/t/changing-content-of-an-array-via-a-function/59771>\
**Category:** New to Julia\
**Tags:** question\
**Created:** [April 22, 2021, 1:50am UTC](https://discourse.julialang.org/t/changing-content-of-an-array-via-a-function/59771 "2021-04-22T01:50:21Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Shuvomoy\_Das\_Gupta](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/shuvomoy_das_gupta/32/10069_2.png) [@Shuvomoy\_Das\_Gupta](https://discourse.julialang.org/u/Shuvomoy_Das_Gupta)\
**Post date:** [April 22, 2021, 1:50am UTC](https://discourse.julialang.org/t/changing-content-of-an-array-via-a-function/59771/1 "2021-04-22T01:50:21Z")

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Dear All,

I am trying to assign values to an array via an index shifting function for a particular reason, I was wondering if there is a way to achieve that in Julia. A simple example is

```julia
a = [1 2 3]
b = [0 0 0] # I want to assign the values of a into b
b_shift(i) = b[i+1] # this shifts the index of b to a zero based index
for i in 0:2
    b_shift(i) = a[i+1] 
    # of course, the straight forward way would be b[i+1] = a[i+1],
    # but I need a index shifter operation for my purpose
    println(b_shift(i)) # output is 1 2 3
end

println(b) # output is [0 0 0], so b did not change

```

Is there a way I can turn `b=a` via the `b_shift` function? Any tips will be appreciated!

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**Author:** ![affans](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/affans/32/11911_2.png) [@affans](https://discourse.julialang.org/u/affans)\
**Post date:** [April 22, 2021, 2:52am UTC](https://discourse.julialang.org/t/changing-content-of-an-array-via-a-function/59771/2 "2021-04-22T02:52:33Z")

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Note that `b_shift(i) = b[i+1]` defines a function that takes the integer `i` and returns `b[i+1]`. But then in your for loop, you have `b_shift(i) = a[i+1] ` which is simply **just overwriting the function definition** (I believe you this is assigning the value of `a[i+1]` to the `b` shifted vector… its not). In order for you to do what you are doing, you’ll need some more machinery by overloading `setindex` and `getindex` functions.

If you want to use a 0-based vector, the best solution would be to use the package `OffsetArrays`.

```julia
using OffsetArrays
a = [1 2 3]
b = [0 0 0] # I want to assign the values of a into b

# create the offsets -- note these are by reference. so modifying a_offset also modifies a
a_offset = OffsetArray(a, 0:2) 
b_offset = OffsetArray(b, 0:2) 
for i in 0:2
    b_offset[i] = a_offset[i] # will modify the original `b` as well.  
end

```

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**Author:** ![Shuvomoy\_Das\_Gupta](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/shuvomoy_das_gupta/32/10069_2.png) [@Shuvomoy\_Das\_Gupta](https://discourse.julialang.org/u/Shuvomoy_Das_Gupta)\
**Post date:** [April 22, 2021, 11:30am UTC](https://discourse.julialang.org/t/changing-content-of-an-array-via-a-function/59771/3 "2021-04-22T11:30:09Z")

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Thanks so much, @affans, your solution works great for my purpose!