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Extract part of a Table with the Wolfram Language?

Hi, I am not an expert with Mathematica, i'm just approaching to this software. I should extract elements from a Table called 'sort', if the first term of the element is equal to a certain value. How can I do this? I have also developed a code, but I don't know how can I implement in Mathematica:

table=Table[{}]
cont=0
cont2=0
For i=1 to npoint
 If sort[[i]][[1]]=sort[[i+1]][[1]] Then
      cont=cont+1
      table=Table[{pippo,sort[[i+1]][[1]]}]
 Elseif cont>0
    cont2=cont2+1
    table(cont2)=table
    Print table(cont2)
    cont=0
 End if
Next i

There is someone who can help me?
POSTED BY: Francesco Pantalone
5 Replies
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POSTED BY: Francesco Pantalone
Gustavo Delfino
Gustavo Delfino
Posted 10 years ago

Francesco, there is an important difference between what you ask and the code you provide. If you just want to select the rows that meed a criteria, using Cases, Select or even Query is the way to go. But you code suggests that to test a line, you need information about the next line. In this case you need to look into using Partition first.

Avoid using the traditional For and While as they almost always lead to solutions more complicated than needed.
POSTED BY: Gustavo Delfino
Bill Simpson
Bill Simpson
Posted 10 years ago

It is difficult to understand exactly how and what to automate.

Perhaps this will help.

Create a concrete example

f = RandomReal[{0, 5}, 6];
unsort = Table[i = RandomInteger[6]; 
y = RandomReal[{0, 10}]; {f[[i]], y}, {1300}];
sort = Sort[unsort]

Now group together all lists which have the same first element

splitsort = Split[sort, First[#1] == First[#2] &]

Now examine the first set of items which share the first element

splitsort[[1]]

Perhaps this will be useful

For[n = 1, n <= Length[splitsort], n++,
 Print["The ", n, "'th group with the same first element is: ", splitsort[[n]]]
 ]

If this is still not sufficient then can you provide the simplest clearest description of what you need as a result? Perhaps with that it will be possible to get closer to what you want to accomplish.
POSTED BY: Bill Simpson

Thanks for your answer. This procedure works, but my problem is to automate the calculation in a loop. In fact I need more or less 1300 extraction for all the different values ??that assumes the first component of each element of the table. These values also include numbers with long decimal points.
POSTED BY: Francesco Pantalone
Bill Simpson
Bill Simpson
Posted 10 years ago
POSTED BY: Bill Simpson
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