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Re: Thread and MapThread

  • To: mathgroup at
  • Subject: [mg29874] Re: [mg29868] Thread and MapThread
  • From: Andrzej Kozlowski <andrzej at>
  • Date: Sun, 15 Jul 2001 00:59:00 -0400 (EDT)
  • Sender: owner-wri-mathgroup at

The problem is that both functions Thread and MapThread evaluate their
arguments. In the case of MapThread and this particular example it is
harmless but it the case of Thread this is what happens:

Thread[ftest[{x1, x2, x3}, {y1, y2, y3}]]//Trace

So what you need to do is:

Thread[Unevaluated[ftest[{x1, x2, x3}, {y1, y2, y3}]]]

Andrzej Kozlowski
Toyama International University

on 01.7.14 2:36 PM, David Park at djmp at wrote:

> Dear MathGroup,
> Here is a function:
> ftest[x_, y_] := {f1[x], f2[y]}
> Why does the following work...
> MapThread[ftest, {{x1, x2, x3}, {y1, y2, y3}}]
> {{f1[x1], f2[y1]}, {f1[x2], f2[y2]}, {f1[x3], f2[y3]}}
> ...but the following does not work.
> Thread[ftest[{x1, x2, x3}, {y1, y2, y3}]]
> {f1[{x1, x2, x3}], f2[{y1, y2, y3}]}
> David Park
> djmp at

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