vectorized if in matlab

Question

I have a boolean array call it flag.

I have two numeric arrays ifTrue, ifFalse. All these arrays are the same size, For purposes of this question assume every element in these arrays is unique.

I would like a function g with the property that

a = g(flag, ifTrue, ifFalse) all(flag == (a == ifTrue)) all(~flag == (a == ifFalse))

Or in English, I would like g to return ifTrue elements when flag is true, and ifFalse elements when flag is false.

Or, in matlab, I could do this with loops:

a = zeros(size(ifTrue)); for i = 1 : numel(ifTrue); if flag(i) a(i) = ifTrue(i) else a(i) = ifFalse(i) end end

Is there a vectorized approach?

Thanks

Edric · Accepted Answer · 2011-12-14 15:00:47Z

%# Given, for example: ifTrue = 1:10 ifFalse = -ifTrue flag = rand(1,10) > 0.5 %# First, set 'a' to ifFalse a = ifFalse %# Then override the places where flag is true a(flag) = ifTrue(flag)

kol · Accepted Answer · 2011-12-14 15:04:15Z

1

Assuming that flag contains ones for true, and zeros for false elements: a = flag .* ifTrue + (1 - flag) .* ifFalse;

answered Dec 14, 2011 at 15:04

kol

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1 Comment

John Over a year ago

It might be worth noting, that this solution doesn't handle Inf's and nan's properly. The accepted answer does handle that case correctly.

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