I've a list where a I want to pick up my first element which matches my criteria. This is my work around:

While[n < Length[listRedPoint],
    If[Sign[listRedPoint[[n]].Take[w, 2] + w[[3]]] != -1, 
    wrongData = {listRedPoint[[n]], -1};

where listRedPoint is a list of m pairs {x_n,y_n}, w is a 3-dimension vector wrongData is the data picked up. In general is there any way to optimize this search-algorithm without use while loop? (Select[]?)

  • $\begingroup$ It seems Select can do what you want, have you tried to use it? $\endgroup$
    – Kuba
    Jun 13, 2016 at 8:58
  • $\begingroup$ I've tried Select[listRedPoint,Sign[#.Take[w, 2] + w[[3]]] != -1,1] but i got an error.... $\endgroup$ Jun 13, 2016 at 9:22
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    – Michael E2
    Jun 13, 2016 at 10:33

1 Answer 1


SelectFirst instead of While-Break.

 Sign[#.Take[w, 2] + Last[w]] > 0 &]
  • $\begingroup$ i suggest also SelectFirst[listRedPoint, Sign[#.Take[w, 2] + Last[w]] > 0 &,1] for users with version <10.... $\endgroup$ Jun 14, 2016 at 19:16

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