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Re: Removing list elements in x by list y

  • To: mathgroup at smc.vnet.net
  • Subject: [mg131142] Re: Removing list elements in x by list y
  • From: Alexei Boulbitch <Alexei.Boulbitch at iee.lu>
  • Date: Fri, 14 Jun 2013 04:59:55 -0400 (EDT)
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I have simple question.

Given two lists

x = {u, v, w, w, d};
y = {u, d};

I wish to "subtract" y from x, i.e. remove exactly the elements in x
which belong to y giving

x "-" y = {v,w,w}

Complement[] gives instead {v,w}.
Note that we are talking about lists rather than sets.

I'm sure there is a simple standard command, but I can't find it.
Can you?

Regards,
Wolfgang

Hi, Wolfgang,

One way to do this is as follows:

x = {u, v, w, w, d};
y = {u, d};

Delete[x, Flatten[Map[Position[x, #] &, y], 1]]

{v, w, w}

This is another, rule-based way:

x /. a_ /; MemberQ[y, a] -> Sequence[]

{v, w, w}

Have fun, Alexei


Alexei BOULBITCH, Dr., habil.
IEE S.A.
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e-mail: alexei.boulbitch at iee.lu






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