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# How to select all elements above the main diagonal of matrix?

How to select all elements above the main diagonal of matrix? I need to create a list of them.

Let's use Span with Part:

mat=RandomInteger[{0, 100}, {5, 5}];

Flatten[mat[[#, # + 1 ;;]] & /@ Range[5]]


n = 4;
m = Array[a, {n, n}];
Join @@ Table[m[[ i, j]], {i, n}, {j, i + 1, n}]

{a[1, 2], a[1, 3], a[1, 4], a[2, 3], a[2, 4], a[3, 4]}


just another way:

Join @@ Pick[
m,
UpperTriangularize[ConstantArray[1, {n, n}], 1],
1]


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# How to select all elements above the main diagonal of matrix?

How to select all elements above the main diagonal of matrix? I need to create a list of them.

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Let's use Span with Part:

mat=RandomInteger[{0, 100}, {5, 5}];

Flatten[mat[[#, # + 1 ;;]] & /@ Range[5]]

Nice, clean, clever, and faster than the naive solution. +1 - rasher Jan 30 at 5:32

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