Filtering a list of strings with list of keywords using loops

Question

I have a list containing strings that contain descriptions from a body of text that looks as follows:

stringlist = ['I have a dog and cat and the dog is seven years old', 'that dog is old']

and I need to filter these strings by a list of keywords that are located in another list:

keywords = ['dog', 'cat', 'old']

and appending each keyword to a row depending on how many times it is located in the string.

filteredlist = [['dog', 'dog', 'cat', 'old'], ['dog', 'old']]

I am splitting the strings in the stringslist and using list comprehension to check if the keyword is in the list but is not outputting correctly when I am looping through the keywords.

The code is working when I use one specific string to search for as follows:

filteritem = 'dog'
filteredlist = []
for string in stringlist:
    string = string.split()
    res = [x for x in string if filteritem in x]
    filteredlist.append(res)

The resulting filteredlist is as follows:

filteredlist = [['dog', 'dog'], ['dog']]

which appends the keyword for each instance that the keyword is located in the string sequence.

When I try looping through the keyword list as follows with a for loop the output loses the structure.

filteredlist = []
for string in stringlist:
    string = string.split()
    for keyword in keywords:
        res = [x for x in string if keyword in x]
        filteredlist.append(res)

Here is the output:

filteredlist =  [['dog', 'dog'], ['cat'], ['old'], [], ['dog'], [], ['old'], []]

I think I'm approaching this problem completely wrong so any other method or solution would be helpful.

I'm not quite clear on what your issue is. Is the filtered_list above what you want the output to look like? — Morgan Thrapp
– Morgan Thrapp, Commented Jun 30, 2015 at 18:49
the filteredlist at the top is the output i want it to look like. — genghistong
– genghistong, Commented Jun 30, 2015 at 18:59

Cory Kramer · Accepted Answer · 2015-06-30 18:49:42Z

3

You can write this as a nested list comprehension

>>> [[word for word in string.split() if word in keywords] for string in stringlist]
[['dog', 'cat', 'dog', 'old'], ['dog', 'old']]

answered Jun 30, 2015 at 18:49

Cory Kramer

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2 Comments

Reut Sharabani Over a year ago

Beat me to it :) You may want to use a set.

genghistong Over a year ago

thanks! knew there had to be a nested list comprehension in there somewhere.

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