Use a any or a all

Question

x   np arange 0 2 0 5  valeur   2 x  if valeur  lt   0 6      print   this works   else         print   valeur is too high     here is the error I get   if valeur  lt   0 6  ValueError  The truth value of an array with more than one element is ambiguous  Use a any   or a all     I have read several posts about a any   or a all   but still can t find a way that really clearly explain how to fix the problem  I see why Python does not like what I wrote but I am not sure how to fix it

User · Answer

This should also work and is a closer answer to what is asked in the question   for i in range len x        if valeur item i   lt   0 6          print   this works       else             print   valeur is too high

User · Answer

You comment      valeur is a vector equal to   0  1  2  3   I am interested in each single term  For the part below 0 6  then return  this works        If you are interested in each term  then write the code so it deals with each   For example   for b in valeur lt  0 6      if b          print   this works       else             print   valeur is too high     This will write 2 lines   The error is produced by numpy code when you try to use it a context that expects a single  scalar  value   if b     can only do one thing   It does not  by itself  iterate through the elements of b doing a different thing for each   You could also cast that iteration as list comprehension  e g     yes  if b else  no  for b in np array  True  False  True

User · Answer

If you take a look at the result of valeur  lt   0 6  you can see what   s causing this ambiguity    gt  gt  gt  valeur  lt   0 6 array   True  False  False  False   dtype bool    So the result is another array that has in this case 4 boolean values  Now what should the result be  Should the condition be true when one value is true  Should the condition be true only when all values are true   That   s exactly what numpy any and numpy all do  The former requires at least one true value  the latter requires that all values are true    gt  gt  gt  np any valeur  lt   0 6  True  gt  gt  gt  np all valeur  lt   0 6  False

[python] Use a.any() or a.all()

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