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Home/ Questions/How to fix "the truth value of an array with more than one element is ambiguous. use a.any() or a.all()"?
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dubuquereta
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dubuquereta
Asked: May 5, 20222022-05-05T03:35:46+00:00 2022-05-05T03:35:46+00:00In: python

How to fix “the truth value of an array with more than one element is ambiguous. use a.any() or a.all()”?

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I’m building a new program, but when I run it, an error pops up. The error displayed is as follows: 

ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

I have tried several workarounds, but they still do not get the desired results. If you have come across this situation and have a solution for the truth value of an array with more than one element is ambiguous. use a.any() or a.all() problem, pls let me know.  This is what I do: 

r = mlab.csv2rec(datafile, delimiter=',', names=COL_HEADERS)
mask = ((r["dt"] >= startdate) and (r["dt"] <= enddate))
selected = r[mask]

Thanks.

numnumpy
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    jgibson
    2022-05-05T04:04:23+00:00Added an answer on May 5, 2022 at 4:04 am

    This error message suggests that you should use a.any() or a.all() instead of the and  operator. However I usually solve this problem using the numpy.logical_and(a,b) method.

    Here is the code after editing

    
     mask = numpy.logical_and(r["dt"] >= startdate, r["dt"] <= enddate)
     selected  = r[mask]
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  2. sipeskaelyn
    2022-05-10T03:33:58+00:00Added an answer on May 10, 2022 at 3:33 am

    Another method I think it is useful:

    • if np.array([]).size: print(1) fixxed the error.
    • You also consider the more pythonic as below:

      if np.array([]) is not None: print(1)

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  3. ewellhomenick
    2022-05-10T03:24:32+00:00Added an answer on May 10, 2022 at 3:24 am

    Simply using a numpy.logical_and(a,b) would work. You could modify the code to be:

    selected = r[numpy.logical_and(r["dt"] >= startdate, r["dt"] <= enddate)]
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