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Re: Selecting table rows


On 4/27/06 at 2:26 AM, skirmantas.janusonis at yale.edu (Skirmantas)
wrote:

>I have a 2D-table whose first column contains the unique identifiers
>(ID) of each row (IDs can be any numbers). I need to delete all rows
>whose IDs are not members of another, control list.

>The following works, but I'm wondering if there is a shorter way to
>do this.

>TBL = {{1, 2, 3, 4}, {5, 6, 7, 8}, {9, 10, 11, 12}, {13, 14, 15,
>16}, {17, 18, 19, 20}};

>CNTR = {1, 9, 17};

>Map[Part[TBL, #]&, Flatten[Map[Position[Transpose[TBL][[1]], #]&,
>CNTR]]]

A shorter way to get the same result would be

In[5]:=
Cases[TBL, {Alternatives @@ CNTR, __}]

Out[5]=
{{1, 2, 3, 4}, {9, 10, 11, 12}, {17, 18, 19, 20}}
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