Re: Generalizing Complement to handle multiple occurrences of elements

• To: mathgroup at smc.vnet.net
• Subject: [mg112466] Re: Generalizing Complement to handle multiple occurrences of elements
• From: Bill Rowe <readnews at sbcglobal.net>
• Date: Thu, 16 Sep 2010 06:01:11 -0400 (EDT)

```On 9/15/10 at 4:38 AM, markspcoleman at gmail.com (Mark Coleman) wrote:

>I'm wondering how one can efficiently generalize the built-in
>Complement function to return multiple occurrences of elements. For
>instance, the current version generates

>a={1,2,2,3,4,4,4,4} b={3,5,7}

>Complement[a,b]={1,2,4}

>I'm looking for a way to define

>myComplement[a,b]={1,2,2,4,4,4,4}

Here are a few ways:

In[3]:= c = Intersection[a, b];
DeleteCases[a, _?(MemberQ[c, #] &)]

Out[4]= {1,2,2,4,4,4,4}

In[5]:= c = Complement[a, b];
Cases[a, _?(MemberQ[c, #] &)]

Out[6]= {1,2,2,4,4,4,4}

In[8]:= Select[a, MemberQ[c, #] &]

Out[8]= {1,2,2,4,4,4,4}

```

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