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Position

WMA link

Position[expr, patt]

returns the list of positions for which expr matches patt.

Position[expr, patt, ls]

returns the positions on levels specified by levelspec ls.

• • Position[{1, 2, 2, 1, 2, 3, 2}, 2]

Find positions upto 3 levels deep:

• • Position[{1 + Sin[x], x, (Tan[x] - y)^2}, x, 3]

Find all powers of x:

• • Position[{1 + x^2, x y ^ 2,  4 y,  x ^ z}, x^_]

Use Position as an operator:

• • Position[_Integer][{1.5, 2, 2.5}]