MathGroup Archive 1997

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Re: selecting from lists

Murray Eisenberg wrote:

> The problem: given an arbitrary list v and a list b of the same
> length, whose entries are all Boolean (True or False), construct a
> function s[v, b] whose result is a list consisting only of those
> entries of v for which the corresponding entries in b are True.  For
> example,
>    v = {3, 82, 7, -12, 5};
>    b = {False, True, True, False};
>    s[v, b]
> {82, 7}

How about

     s[v_, b_] := Cases[Transpose[{v, b}], {x_, True} -> x]
--Lou Talman

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