Defining an array(C) in Julia by appending array B to array A without changing the values of the arr-CodePudding

I have two arrays A and B. Let's say A=[1,2,3] and B=[4,5,6]. I want to define a third array C = append!(A,B). The problem is this also changes A to be A=[1,2,3,4,5,6]. How to avoid this problem?

CodePudding user response：

append! pushes the elements of the second collection to the first one, modifying it, to just concatenate them, use vcat:

C = vcat(A, B)

Or you can use ; to build a new array from the contents of A and B:

C = [A ; B]

CodePudding user response：

You could try this:

A=[1,2,3]
B=[4,5,6]

C=A
append!(C,B)

Then C = [1,2,3,4,5,6] and B = [4,5,6]. But unfortunately, A = [1,2,3,4,5,6].

The problem is C=A, which makes A and C the same in every way, except for the variable name. Unfortunately, changes to C then also change A, because they occupy the same area of memory, they have the same address.

What you have to do is to copy A to C, before appending B. Then C and A have the same data, before B is appended, but they are separate things. Changing C no longer changes A.

 A = [1,2,3]
 B = [4,5,6]

 C=copy(A)
 append!(C,B)

Then C = [1,2,3,4,5,6] and B = [4,5,6]. And, A = [1,2,3].