Copying one row of a 2D array to a 1-dimensional array.

[AndrewMozley]

I have a 2-dimensional of 3 columns by 4 rows. So :

ArrayA = {{x11,x12,x13},{x21,x22,x23},{x31,x32,x33},{x41,x42,x43}}
That is : ArrayA[1,3] = x13, ArrayA[3,2] = x32 . . . .&c

I want to copy one row (for example the 2nd row) of this array to a one dimensional array, ArrayB, so that ArrayB[1] = x21, ArrayB[2] = x22, ArrayB[3] = x23. How do I do this please?

Thanks. Andrew

 

[Olaf Doschke]

1. Dimension a destination array 1-D
2. ACOPY(sourcearrayname,destinationarrayname,firstsourceelement,numberofelements,firstdestinationelement)

You need to know you can always address a 2-D array as a 1-D array, too. This means elements of the second row are either [2,1] to [2,3] or [4]-[6].
This may even be simple enough, compute (row-1)*columns+col and you have firstelement, in this case that is (2-1)*3+col = 3+col, as said: 4 to 6.
Number of array elements obviously is 3 and first element of the destination array of course 1, you want to copy into the start of the new arra.

DIMENSION ArrayB[3]
ACOPY(ArrayA,ArrayB,4,3,1)

Tested:

Dimension ArrayA[4,3]
ArrayA[2,1]=21
ArrayA[2,2]=22
ArrayA[2,3]=23

Dimension ArrayB[3]
Acopy(ArrayA,ArrayB,4,3,1)
? ArrayB[1]
? ArrayB[2]
? ArrayB[3]

If you would want to copy a column, that would be harder to do, but obviously you can always do a FOR loop to iterate the elements you want.

Bye, Olaf.

 

[AndrewMozley]

Thanks Olaf. That sets my mind at rest!

I think I was thinking of the old Clipper facilities, where you could refer to (all the elements) of a row of a 2D array and copy them into a 1-D array in (more or less) a single instruction.

But what you have explained is clear and effective. Thanks again.

 

[Olaf Doschke]

Well, two lines is not much, is it? And ACOPY could also create the destination array, but you obviously have more control about its size, if you predefine it.

EDIT - To explain why control matters here:
At some points of the ACOPY help topic the help says the automatically created array will have the same size as the source array, which obviously would be wrong, if you want the destination array to be one dimensional. So control about the dimensioning of the destination array matters.

Bye, Olaf.