How to get Diagonal elements of a 2d Array converted to 1D (linear indexing use)?

[analog mica]

hii 👋 i am trying to get diagonal elements of a 2d array with 1d indexing and was able to get the top-left to bottom-right of the array using the r * colNum + c, but i am having trouble with getting the formula for the top-right to bottom-left diagonal.

i've tried r * (colNum - 1 - c) but it did not work:
16 2 3 13 5 11 10 8 9 7 6 12 4 14 15 1

the formula gives me 16 3 3 16

anyone knows what the correct formula for the top-right -> bottom-left diagonal is?

thank you in advance!🙏

[foggy sparrow]

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[dawn flint]

I have no clue why anyone would ever want to have that diagonal (don't get me wrong, top-left to bottom-right is insanely useful, but top-right to bottom-left kinda isn't).
Nonetheless, all you have to do is let c run from colNum - 1 to 0 instead of from 0 to colNum - 1.

Otherwise if you insist on letting c run from 0 upwards you just have to "invert" it in your equation: r * colNum + ((colNum - 1) - c)

[analog mica]

thank you again!

!close