CODEWITHSUNDEEP
pythonpandasregexperformanceoptimization
blackmamba
blackmamba

Reputation: 15

Regex in python dataframe: count occurences of pattern

I want to count how often a regex-expression (prior and ensuing characters are needed to identify the pattern) occurs in multiple dataframe columns. I found a solution which seems a litte slow. Is there a more sophisticated way?

column_A column_B column_C
Test • test abc winter • sun snow rain blank
blabla • summer abc break • Data test letter • stop.

So far I created a solution which is slow:

print(df["column_A"].str.count("(?<=[A-Za-z]) • (?=[A-Za-z])").sum() + df["column_B"].str.count("(?<=[A-Za-z]) • (?=[A-Za-z])").sum() + df["column_C"].str.count("(?<=[A-Za-z]) • (?=[A-Za-z])").sum())

Upvotes: 1

Views: 225

Answers (2)

user16836078
user16836078

Reputation:

The str.count should be able to apply to the whole dataframe without hard coding this way. Try

sum(df.apply(lambda x: x.str.count("(?<=[A-Za-z]) • (?=[A-Za-z])").sum()))

I have tried with 1000 * 1000 dataframes. Here is a benchmark for your reference.

%timeit sum(df.apply(lambda x: x.str.count("(?<=[A-Za-z]) • (?=[A-Za-z])").sum()))
1.97 s ± 54.4 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)

Upvotes: 1

I&#39;mahdi
I&#39;mahdi

Reputation: 24059

You can use list comprehension and re.search. You can reduce 938 µs to 26.7 µs. (make sure don't create list and use generator)

res = sum(sum(True for item in df[col] if re.search("(?<=[A-Za-z]) • (?=[A-Za-z])", item))
       for col in ['column_A', 'column_B','column_C'])
print(res)
# 5

Benchmark:

%%timeit 
sum(sum(True for item in df[col] if re.search("(?<=[A-Za-z]) • (?=[A-Za-z])", item)) for col in ['column_A', 'column_B','column_C'])
# 26 µs ± 2.2 µs per loop (mean ± std. dev. of 7 runs, 10000 loops each)

%%timeit 
df["column_A"].str.count("(?<=[A-Za-z]) • (?=[A-Za-z])").sum() + df["column_B"].str.count("(?<=[A-Za-z]) • (?=[A-Za-z])").sum() + df["column_C"].str.count("(?<=[A-Za-z]) • (?=[A-Za-z])").sum()
# 938 µs ± 149 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)
# --------------------------------------------------------------------#

Upvotes: 0

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