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I'm trying to extract either the first (or only) floating point or integer from strings like these:

str1 = np.asarray('92834.1alksjdhaklsjh')
str2 = np.asarray'-987___-')
str3 = np.asarray'-234234.alskjhdasd')

where, if parsed correctly, we should get

var1 = 92834.1   #float
var2 = -987      #int 
var3 = -234234.0 #float

Using the "masking" property of numpy arrays I come up with something like for any of the str_ variables, e.g.:

>> ma1 = np.asarray([not str.isalpha(c) for c in str1.tostring()],dtype=bool)

array([ True,  True,  True,  True,  True,  True,  True, False, False,
     False, False, False, False, False, False, False, False, False,
     False, False], dtype=bool)

>> str1[ma1]

IndexError: too many indeces for array

Now I've read just about everything I can find about indexing using boolean arrays; but I can't get it to work.

It's simple enough that I don't think hunkering down to figure out a regex for is worth it, but complex enough that it's been giving me trouble.

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  • Similar algorithm without numpy - ''.join([c for c in s if not c.isalpha()]) . But please note this in no way takes out the first float/int if there are multiple places where digits exist in the string.
    – Anand S Kumar
    Sep 23, 2015 at 7:12
  • I think you can use a ^.*?([+-]?\d*\.?\d+) regex here. Does it work for you?
    – Wiktor Stribiżew
    Sep 23, 2015 at 7:20
  • @stribizhev - Impressive with the regex (a fear of mine) but for the example you linked, it returns an int, when it needs to return a parsed float. For my application, getting the type correct is important. I modified your script to show what I mean.
    – user27886
    Sep 23, 2015 at 8:12
  • I think that -234234 is an int, not a float. You asked to extract either integer or floats. If you only need floats, use Kasra's version.
    – Wiktor Stribiżew
    Sep 23, 2015 at 8:15

1 Answer 1

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You can not create an array with different type like that, If you wan to use different types in a numpy array object you might use a record array and specify the types in your array but here as a more straight way you can convert your numpy object to string and use re.search to get the number :

>>> float(re.search(r'[\d.-]+',str(str1)).group())
92834.1
>>> float(re.search(r'[\d.-]+',str(str2)).group())
-987.0
>>> float(re.search(r'[\d.-]+',str(str3)).group())
-234234.0

But if you want to use a numpy approach you need to first create an array from your string :

>>> st=str(str1)
>>> arr=np.array(list(st))
>>> mask=map(str.isalpha,st)
>>> mask
[False, False, False, False, False, False, False, True, True, True, True, True, True, True, True, True, True, True, True, True]

>>> arr[~mask]
array(['9', '2', '8', '3', '4', '.', '1'], 
      dtype='|S1')

And then use str.join method with float:

>>> float(''.join(arr[~mask]))
92834.1
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