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I have data of the following form 

data={{6, 23.3}, {6.1, 19.8}, {6.2, 25.1}, {6.3, 25.5}, {6.4, 24.5}, {6.5, 
  28.1}, {6.6, 24.9}, {6.7, 26.3}, {6.8, 27.3}, {6.9, 27.7}, {7, 
  33.9}, {7.1, 26.6}, {7.2, 31.3}, {7.3, 26.8}, {7.4, 31.5}, {7.5, 
  30.2}, {7.6, 29.8}, {7.7, 25.5}, {7.8, 31.5}, {7.9, 28.9}, {8, 
  28.1},...,}

This is a very long list of pairs, which are of the form $(t,B)$, time and magnetic field magnitude. Then I used a code to find relevant points that I need to use. Namely the peaks of the magnetic field. With the help of FindPeak I found that the Peak Magnetic moments are 

peaks={{15, 31.5}, {99, 31.6}, {170, 45.7}, {224, 15.7}, {281, 15.6}, {319, 
  13.1}, {345, 10.5}, {349, 11.1}, {437, 8.4}}

I also found the corresponding time using peaktime = data[[First /@ peaks, 1]]

What I wish is to create a list of pairs, of the form $(t_p,B_p)$ such that $t_p$ and $B_p$ are the peak times and magnetic field magnitudes, respectively. For this I used a For loop, which is the following:

v = {};
For[i = 1, i <= Length[peaktime], i++, 
 u = Position[data[[All, 1]], peaktime[[i]]][[1]]; 
 v = Union[v, u]]
peakscouuple = data[[v, All]];

This works, but it is too messy, Is there a cleaner way to do this?

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  • 1
    $\begingroup$ A minimum working example would be useful ... $\endgroup$ – user1066 Mar 16 at 19:04
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    $\begingroup$ If I understand you correctly, you can just use data[[First/@peaks]] without the spec to take the first part like you used in peaktime=data[[...,1]] to get (t,B) pair corresponding to the peaks. $\endgroup$ – N.J.Evans Mar 16 at 19:04
  • $\begingroup$ You could also use Extract[data,Position[PeakDetect[Last/@data],1]]. $\endgroup$ – N.J.Evans Mar 16 at 19:09
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data = {{6, 23.3}, {6.1, 19.8}, {6.2, 25.1}, {6.3, 25.5}, {6.4, 24.5}, {6.5, 28.1},
  {6.6, 24.9}, {6.7, 26.3}, {6.8, 27.3}, {6.9, 27.7}, {7, 33.9}, {7.1, 26.6}, 
  {7.2, 31.3}, {7.3, 26.8}, {7.4, 31.5}, {7.5, 30.2}, {7.6, 29.8}, {7.7, 25.5}, 
  {7.8, 31.5}, {7.9, 28.9}, {8, 28.1}};

Pick[data, PeakDetect[data[[All, 2]]], 1]

{{6, 23.3}, {6.5, 28.1}, {7, 33.9}, {7.2, 31.3}, {7.4, 31.5}, {7.8, 31.5}}

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data[[FindPeaks[data[[All, 2]]][[All, 1]]]]
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