Count how often a specific string occurs in a list

Question

I want to pairwise compare several lists in a kind of "bag of words" approach. I have only strings in my lists.
Unfortunatelly, I have a bug in my script that I cannot fix.
The code works if there are numbers in the lists but as soon as I have strings in the lists it doesn't run anymore. I appreciate your help.

I receive following error message:

Traceback (most recent call last):
File "test.py", line 21, in <module>
bow_matrix[0, p] = list_words_ab[p]
ValueError: could not convert string to float: 'd'

My code:

a = ["a", "b", "c", "d"]
b = ["b", "c", "d", "e"]

p = 0
if len(a) > len(b):
    max_words = len(a)
else:
    max_words = len(b)
list_words_ab = list(set(a) | set(b))
len_bow_matrix = len(list_words_ab)
bow_matrix = numpy.zeros(shape = (3, len_bow_matrix))

while p < len_bow_matrix:
    bow_matrix[0, p] = list_words_ab[p]
    p = p+1
p = 0
while p < len_bow_matrix:
    bow_matrix[1, p] = a.count(bow_matrix[0, p])
    bow_matrix[2, p] = b.count(bow_matrix[0, p])
    p = p+1

For example a = [NLS, VS40, AMPR], b = [VS40, VS40, AMPR, GFP] I want to get a matrix that looks like this: [ [NLS, VS40, AMPR, GFP], [1, 1, 1, 0], [0, 2, 1, 1] ] In the first row there is the union of all strings in both list (without duplicates) and in row two/three I want to have the frequency how often that string occurs in list a/b. — Philipp
– Philipp, Commented Aug 23, 2016 at 20:09
I believe using numpy.zeros creates a matrix that expects floats. — Matt Cremeens
– Matt Cremeens, Commented Aug 23, 2016 at 20:11

Tadhg McDonald-Jensen · Accepted Answer · 2016-08-23 20:12:01Z

3

By default numpy.zeros makes an empty array of floats, to use strings you need to specify dtype=str:

bow_matrix = numpy.zeros(shape = (3, len_bow_matrix),dtype=str)

answered Aug 23, 2016 at 20:12

Tadhg McDonald-Jensen

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1 Comment

hpaulj Over a year ago

dtype=str only makes S1, single character words. Which is fine here, but not in more general cases.

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