CODEWITHSUNDEEP
arrayspointersjulia
sayeg84
sayeg84

Reputation: 117

Make sum of int array change with changes in array elements

I have an collection of arrays of the following way:

arr = Array{Array{Int64,1},1}( [ [1,2,3] , [4,5,6] , [7,8,9] ] )

I want to define a new aray sum such that sums[i] = sum(arr[i]) but in a dynamic way such that if I change an element of arr[i], sums[i] changes automatically. For example:

julia> sums
3-element Array{Int64,1}:
  6
 15
 24

julia> arr[1][1] = 3
3

julia> sums
3-element Array{Int64,1}:
  8
 15
 24

Is this possible to do? If so, how can I do it?

Upvotes: 0

Views: 66

Answers (1)

hckr
hckr

Reputation: 5583

You can use MappedArrays. MappedArrays provide a "view" M of an array A so that M[i] = f(A[i]). All you need to do add MappedArrays package by ]add MappedArrays and start using it with sum function. Note that the transformation is lazy, meaning that it will compute the values in M when you try to access them. Therefore, after an update to A, you will see the change in M when you access entries of M.

julia> using MappedArrays

julia> arr = [ [1,2,3] , [4,5,6] , [7,8,9] ] 
3-element Array{Array{Int64,1},1}:
 [1, 2, 3]
 [4, 5, 6]
 [7, 8, 9]

julia> M = mappedarray(sum, arr)
3-element mappedarray(sum, ::Array{Array{Int64,1},1}) with eltype Int64:
  6
 15
 24

julia> arr[1][2] = 10
10

julia> M
3-element mappedarray(sum, ::Array{Array{Int64,1},1}) with eltype Int64:
 14
 15
 24

Upvotes: 1

Related Questions