Re: Select list elements and exchange them
- To: mathgroup at smc.vnet.net
- Subject: [mg109820] Re: Select list elements and exchange them
- From: Bill Rowe <readnews at sbcglobal.net>
- Date: Wed, 19 May 2010 07:02:31 -0400 (EDT)
On 5/18/10 at 6:12 AM, ishii.mitsuo.titanium at nsc.co.jp wrote:
>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.
either
In[5]:= Cases[testList, {_, {3, 4}}]
Out[5]= {{21, {3, 4}}}
or
In[6]:= Select[testList, Last@# === {3, 4} &]
Out[6]= {{21, {3, 4}}}
will do this
>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}} }
This last can be accomplished in one step as:
In[7]:= testList /. {_, {3, 4}} -> {100, {3, 4}}
Out[7]= {{11, {2, 3}}, {100, {3, 4}}, {34, {5, 6}},
{51, {7, 8}}}