How do I extract elements from a table according to specific conditions?

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Kyle Davis 2019-5-24

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评论： Kyle Davis 2019-5-25

Hi,

I am trying to extract certain rows of data from the following table (T1) according to specfic conditions. I only want to extract a row if 'TargetStatus' is equal to 'T' and t the same time, 'Response' is equal to 'k' (such as row 2 and row 7 for example). I'm struggling to come up with the correct code that will allow me to do this. I have copied the table below :)

T1 =
  24×4 table
    Sequence    TargetStatus    ReactionTime    Response
    ________    ____________    ____________    ________
      'C'           'N'            1.1022         'j'   
      'C'           'T'            1.4261         'k'   
      'T'           'N'           0.77136         'j'   
      'D'           'N'           0.77733         'j'   
      'K'           'N'             1.044         'j'   
      'X'           'N'            1.0333         'j'   
      'X'           'T'           0.82694         'k'   
      'B'           'N'           0.89246         'j'   
      'W'           'N'           0.86045         'j'   
      'H'           'N'           0.73916         'j'   
      'H'           'T'           0.84648         'k'   
      'T'           'N'           0.91134         'j'   
      'T'           'T'           0.91947         'k'   
      'G'           'N'           0.70199         'j'   
      'G'           'T'           0.81821         'k'   
      'Z'           'N'           0.79684         'j'   
      'Q'           'N'           0.94614         'j'   
      'J'           'N'           0.83011         'j'   
      'Z'           'N'           0.85475         'j'   
      'F'           'N'           0.72073         'j'   
      'F'           'T'           0.64145         'k'   
      'B'           'N'           0.66913         'j'   
      'X'           'N'           0.71484         'j'   
      'X'           'T'            0.8122         'k' 

Thank you to anyone who is able to help :)

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Answer 1

Jeff Miller 2019-5-25

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I think if you want to select rows then the colon operator is in the wrong place, and that you would want something like

T1(strcmp(T1.TargetStatus, 'T') & strcmp(T1.Response, 'k'),:);

But it might really be more convenient to use categorical variables, like this

T1.Sequence = categorical(T1.Sequence)
T1.TargetStatus = categorical(T1.TargetStatus)
T1.Response = categorical(T1.Response)
T1(T1.TargetStatus=='N' & T1.Response=='k',:)

Since you are analyzing RT data, you might find the RawRT toolbox useful. It won't work with categorical variables, so you would have to convert everything to numbers, like this:

T1.Sequence = grp2idx(T1.Sequence);
T1.TargetStatus = grp2idx(T1.TargetStatus);
T1.Response = grp2idx(T1.Response);

But then you could compute a lot of summary stats, graphs, ANOVAs, etc pretty simply, e.g.

somemeans = CondMeans(T1,'ReactionTime',{'TargetStatus','Response'})  % which produces
somemeans = 
    TargetStatus    Response    ReactionTime
    ____________    ________    ____________
    1               1           0.84507     
    2               2           0.89869     

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Kyle Davis 2019-5-25

Thank you so much, your solution using categorical variables worked!! Really appreciate your help :)

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Answer 2

Guillaume 2019-5-24

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T1(:, T1.TargetStatus == 'N'  & T1.Response == 'k')  %select all rows for which TargetStatus is 'N' AND Response is 'k'

Note that == works here because your char arrays are just one character. If they had more than one character, you'd use strcmp instead.

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Kyle Davis 2019-5-24

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Thank you for your response.

I have tried to use your suggestion, however Matlab produces the following error:

"Undefined operator '==' for input arguments of type 'cell' ".

T1(:, T1.TargetStatus == 'T' & T1.Response == 'k');
Undefined operator '==' for input arguments of type
'cell'.

Sorry, I didn't realise that the data was type 'cell'.

In this case, would I have to use the 'strcmp' command as you previously mentioned? If so how would I implement that into the code? I've played around with it but can't seem to get it to do what I want it to!

Thanks :)