'Subsetting pandas dataframe if column contains only ONE instance of string

I have the following data frame, I only want to grab rows where the summary column only contains ONE instance of '->'. How can I do this in pandas?

Input:

idx  summary
0    McDonalds -> Wendys -> Popeyes
1    Popeyes -> Taco Bell
2    Carls Jr -> Arbys
3    Arbys -> Popeyes -> Taco Bell -> KFC
4    KFC -> Popeyes -> Boston Market

Expected Output:

idx  summary
1    Popeyes -> Taco Bell
2    Carls Jr -> Arbys

python pandas

Solution 1:^[1]

str.count('->')==1 will grab the -> that occurs only once. Using the loc helps to identify which row it is located in, so the expected results will be the actual message, instead of True or False.

df_new = pd.DataFrame(df.loc[df["summary"].str.count('->')==1])
print(df_new)

Solution 2:^[2]

If your input is saved as variable df, this would produce that result:

ct_arrow = df.apply(lambda x: x.summary.count('->'), axis=1)
df = df.loc[ct_arrow==1]
print(df)

Solution 3:^[3]

You can do that with the following

df[df["summary"].str.count('->')==1]

Solution 4:^[4]

As @mozway suggested, use your previous dataframe as starting point:

>>> df
  first_stop  second_stop     third_stop
0  mcdonalds  burger king        popeyes
1  mcdonalds          N/A            N/A
2     wendys          kfc            N/A
3  taco bell          kfc         wendys
4    popeyes          kfc  panda express

>>> df[df.replace('N/A', pd.NA).count(axis=1).eq(2)]
  first_stop second_stop third_stop
2     wendys         kfc        N/A

Sources

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Source: Stack Overflow

Solution	Source
Solution 1
Solution 2	AlecZ
Solution 3	BoomBoxBoy
Solution 4	Corralien

'Subsetting pandas dataframe if column contains only ONE instance of string

Solution 1:[1]

Solution 2:[2]

Solution 3:[3]

Solution 4:[4]

Sources

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