python find string pattern in numpy array of strings

Question

I have a numpy array of strings 'A' of length 100 and they are sentences of different sizes. It is string NOT numpy strings

>>> type(A[0])
<type 'str'>

I want to find the location of strings in A which contain certain pattern like 'zzz' in them.

I tried

np.core.defchararray.find(A, 'zzz')

gives error:

TypeError: string operation on non-string array

I assume I will need to change each of the 'str' in A to numpy string ?

Edit:

I want to find the index of 'zzz' appearance in A

Answer 1

No need to be fancy with this, you can get the list of indicies with a list comprehension and the in operator:

>>> import numpy as np
>>> lst = ["aaa","aazzz","zzz"]
>>> n = np.array(lst)
>>> [i for i,item in enumerate(n) if "zzz" in item]
[1, 2]

Note that here the elements of the array are actually numpy strings, but the in operator will work for regular strings too, so it's moot.

Answer 2

The issue here is the nature of your array of strings.

If I make the array like:

In [362]: x=np.array(['one','two','three'])

In [363]: x
Out[363]: 
array(['one', 'two', 'three'], 
      dtype='<U5')

In [364]: type(x[0])
Out[364]: numpy.str_

The elements are special kind of string, implicitly padded to 5 characters (the longest, 'np.char methods work on this kind of array

In [365]: np.char.find(x,'one')
Out[365]: array([ 0, -1, -1])

But if I make a object array that contains strings, it produces your error

In [366]: y=np.array(['one','two','three'],dtype=object)

In [367]: y
Out[367]: array(['one', 'two', 'three'], dtype=object)

In [368]: type(y[0])
Out[368]: str

In [369]: np.char.find(y,'one')
...
/usr/lib/python3/dist-packages/numpy/core/defchararray.py in find(a, sub, start, end)
...
TypeError: string operation on non-string array

And more often than not, an object array has to be treated as a list.

In [370]: y
Out[370]: array(['one', 'two', 'three'], dtype=object)

In [371]: [i.find('one') for i in y]
Out[371]: [0, -1, -1]

In [372]: np.array([i.find('one') for i in y])
Out[372]: array([ 0, -1, -1])

The np.char methods are convenient, but they aren't faster. They still have to iterate through the array applying regular string operations to each element.

Answer 3

you can try this one:

np.core.defchararray.find(A.astype(str), 'zzz')