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Re: Replace specific element with specific value.

  • To: mathgroup at smc.vnet.net
  • Subject: [mg99723] Re: Replace specific element with specific value.
  • From: Bill Rowe <readnews at sbcglobal.net>
  • Date: Tue, 12 May 2009 03:09:22 -0400 (EDT)

On 5/11/09 at 6:22 AM, nick.maj at mssm.edu wrote:

>Let me elaborate on this problem again with numbers only.

>data = {{0, 2}, {2, 3}, {3, 4}, {4, 6}, {6, 8}, {8, 9}, {9, 10}}

>positionList = {3, 6, 7}

>replacementList = {8, 17, 25}

>needed output:

>{{0, 2}, {2, 3}, {3, 8}, {4, 6}, {6, 8}, {8, 17}, {9, 25}}

>Based on the positionList - replacementList information, the
>function must replace the 2nd element in the 3rd, 6th and 7th list
>of data with the value 8, 17 and 25 respectively.

Here is one way:

In[6]:= ReplacePart[data,
  Thread[Evaluate[{#, 2} & /@ positionList] -> replacementList]]

Out[6]= {{0, 2}, {2, 3}, {3, 8}, {4, 6}, {6, 8}, {8, 17}, {9, 25}}

Note, the output is what you want and the original list is
unchanged. That is:

In[7]:= data

Out[7]= {{0, 2}, {2, 3}, {3, 4}, {4, 6}, {6, 8}, {8, 9}, {9, 10}}

Obviously, if you want the original list changed all you need do
is set the original list to the output.



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