2
$\begingroup$

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?

Improve this question
$\endgroup$
3
  • 1
    $\begingroup$ A minimum working example would be useful ... $\endgroup$
    – user1066
    Mar 16, 2020 at 19:04
  • 3
    $\begingroup$ 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, 2020 at 19:04
  • $\begingroup$ You could also use Extract[data,Position[PeakDetect[Last/@data],1]]. $\endgroup$
    – N.J.Evans
    Mar 16, 2020 at 19:09

2 Answers 2

Reset to default
5
$\begingroup$ 
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}}

Improve this answer
$\endgroup$
2
$\begingroup$ 
data[[FindPeaks[data[[All, 2]]][[All, 1]]]]
Improve this answer
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.