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Re: Select list elements and exchange them

  • To: mathgroup at smc.vnet.net
  • Subject: [mg109810] Re: Select list elements and exchange them
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Wed, 19 May 2010 07:00:42 -0400 (EDT)

testList = {{11, {2, 3}}, {21, {3, 4}}, {34, {5, 6}}, {51, {7, 8}}, {77, {3, 
     4}}};

Cases[testList, {_, {3, 4}}]

{{21, {3, 4}}, {77, {3, 4}}}

or

Select[testList, #[[2]] == {3, 4} &]

{{21, {3, 4}}, {77, {3, 4}}}

Flatten[Position[testList, {_, {3, 4}}]]

{2,5}

However, none of this is needed. Just use

testList /. {_, {3, 4}} -> {100, {3, 4}}

{{11, {2, 3}}, {100, {3, 4}}, 
   {34, {5, 6}}, {51, {7, 8}}, 
   {100, {3, 4}}}


Bob Hanlon

---- ishii.mitsuo.titanium at nsc.co.jp wrote: 

=============
Hi

I have a problem.


I have a list.

testList={ {11,{2,3}},{21,{3,4}},{34,{5,6}},{51,{7,8}} }

1) From this list, select any element list such as {x,{3,4}},

 where X is an arbitrary number. 

In general, position of {x,{3,4}} in "testList" is not fixed.

2) Select any element list such as {x,{3,4}} and then  exchange {x,{3,4}} to {100,{3,4}}.

3)Make a new list finally. 

testListNew={ {11,{2,3}},{100,{3,4}},{34,{5,6}},{51,{7,8}} }

Please teach me how to solve.

Thanks in advance.

Mitsuo Ishii




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