Convert an numpy array with header to float

Question

I wanted to use the function .astype(float) to convert an array named Defocus_Array to float. But I got this error.

>>> Defocus_Array.astype(float)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: could not convert string to float: defocus

I understand that "defocus" the name of the data extracted is the problem. I tried to delete it with numpy.delete but it doesn't work. How can I delete it to convert my array? Or is it another way to convert my array? Thank you.

What do you want to do with the element containing "defocus"? Do you want it to become nan? Then just assign those values to 'nan' and they will convert to nan. — Frank M
– Frank M, Commented Nov 27, 2014 at 16:31

Frank M · Accepted Answer · 2014-11-27 16:40:41Z

1

Defocus_Array = np.array(('123.3', '0', 'defocus'))
Defocus_Array.astype(float)  # ValueError: could not convert string to float: defocus

Defocus_Array[2] = 'nan'
Defocus_Array.astype(float)  # array([ 123.3,    0. ,    nan])

Or, more generally:

Defocus_Array[Defocus_Array == 'defocus'] = 'nan'
Defocus_Array.astype(float)

Or, if you just want to ignore 'defocus' values:

Defocus_Array[Defocus_Array != 'defocus'].astype(float)

edited Nov 27, 2014 at 16:40

answered Nov 27, 2014 at 16:34

Frank M

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1 Comment

Coug Over a year ago

Thank you, it's exactely what I want!

Kirill Zaitsev · Accepted Answer · 2014-11-27 16:38:35Z

1

You can write a function, that applies to a whole array like this:

def safe_float(f, default=0):
    try:
        return float(f) 
    except ValueError:
        return default

print z
## ['0' '1' '2' '3' '4' '5' '6' '7' '8' '9' 'foo']
numpy.vectorize(safe_float)(z)
## array([ 0.,  1.,  2.,  3.,  4.,  5.,  6.,  7.,  8.,  9.,  0.])

answered Nov 27, 2014 at 16:38

Kirill Zaitsev

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