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up vote 4 down vote favorite

I'm using a numpy object_ array to store variable length strings, e.g.

a = np.array(['hello','world','!'],dtype=np.object_)

Is there an easy way to find the length of the longest string in the array without looping over all elements?

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4 Answers 4

up vote 4 down vote accepted

max(a, key=len) gives you the longest string (and len(max(a, key=len)) gives you its length) without requiring you to code an explicit loop, but of course max will do its own looping internally, as it couldn't possibly identify "the longest string" in any other way.

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1  
Great answer!!! – Tristan Forward Aug 28 '14 at 23:12
up vote 1 down vote

If you store the string in a numpy array of dtype object, then you can't get at the size of the objects (strings) without looping. However, if you let np.array decide the dtype, then you can find out the length of the longest string by peeking at the dtype:

In [64]: a = np.array(['hello','world','!','Oooh gaaah booo gaah?'])

In [65]: a.dtype
Out[65]: dtype('|S21')

In [72]: a.dtype.itemsize
Out[72]: 21
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up vote 0 down vote

No as the only place the length of each string is known is by the string. So you have to find out from every string what its length is.

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up vote 0 down vote

Say I want to get the longest string in the second column:

data_array = [['BFNN' 'Forested bog without permafrost or patterning, no internal lawns']
             ['BONS' 'Nonpatterned, open, shrub-dominated bog']]


def get_max_len_column_value(data_array, column):
    return len(max(data_array[:,[column]], key=len)[0])

get_max_len_column_value(data_array, 1)

>>>64
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