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}}}