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MathGroup Archive 2004

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RE: DeleteCases : several at once, conditions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg49385] RE: [mg49369] DeleteCases : several at once, conditions
  • From: "David Park" <djmp at earthlink.net>
  • Date: Sat, 17 Jul 2004 06:38:51 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Use Alternatives (the upright bar that is the capital \ on the keyboard) to
enter several patterns.

list = {{1, 6, 7}, {3, 6, 9}, {1, 2, 11}, {3, 5, 9}, {2, 5, 6}, {2, 9,
        11}, {2, 10, 11}, {3, 7, 9}, {5, 8, 11}, {3, 7, 9}, {7, 8, 9}, {2,
5,
        12}, {2, 6, 10}, {2, 10, 11}, {1, 6, 9}, {6, 10, 12}, {3, 6, 12},
{2,
        5, 12}, {3, 8, 9}, {1, 2, 7}};
Length[list]
20

DeleteCases[list, {1, _, _} | {9, _, _}]
Length[%]
{{3, 6, 9}, {3, 5, 9}, {2, 5, 6}, {2, 9, 11}, {2, 10, 11}, {3, 7, 9}, {5, 8,
    11}, {3, 7, 9}, {7, 8, 9}, {2, 5, 12}, {2, 6, 10}, {2, 10, 11}, {6, 10,
    12}, {3, 6, 12}, {2, 5, 12}, {3, 8, 9}}
16

To check the cases deleted (there were no cases with leading 9)...

Cases[list, {1, _, _} | {9, _, _}]
{{1, 6, 7}, {1, 2, 11}, {1, 6, 9}, {1, 2, 7}}

To delete all cases that contain an even number...

DeleteCases[list, {___, _?EvenQ, ___}]
{{3, 5, 9}, {3, 7, 9}, {3, 7, 9}}

The triple break characters mean zero or more items, so the pattern picks
out all cases that contain at least one even number.

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/







From: camerzone [mailto:camerzone at yahoo.com]
To: mathgroup at smc.vnet.net

Suppose you have a list of lists, something like
{{1, 6, 7}, {3, 6, 9}, {1, 2, 11}, {3, 5, 9}, {2, 5, 6}, {2, 9, 11}, {
  2, 10, 11}, {3, 7, 9}, {5, 8, 11}, {3, 7, 9}, {7, 8, 9}, {2, 5, 12},
{2, 6,
    10}, {2, 10, 11}, {1, 6, 9}, {6, 10, 12}, {3, 6, 12}, {2, 5, 12},
{3, 8,
     9}, {1, 2, 7}}
and you want to delete cases matching several different patterns, say
{1,_,_} and {9,_,_}
What's the most efficient way?

Also, can you use conditions with DeleteCases?  Say, I want to delete
all cases containing even numbers?

tks




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