Python: In a DataFrame, how do I loop through all strings of one column and check to see if they appear in another column and count them?

Question

I've got a dataframe and want to loop through all cells within column c2 and count how many times each entire string appears in another column c1 , if it exists. Then print the results.

Example df:

id     c1                c2
0      luke skywalker    han solo
1      leia organa       r2d2
2      darth vader       finn
3      han solo          the emporer
4      han solo          c3po
5      finn              leia organa
6      r2d2              darth vader

Example printed result:

han solo      2
r2d2          1
finn          1
the emporer   0
c3po          0
leia organa   1
darth vader   1

I'm using Jupyter notebook with python and pandas. Thanks!

Answer 1

You can use some Numpy magic.
Use count and broadcasting to compare each combination.

from numpy.core.defchararray import count

c1 = df.c1.values.astype(str)
c2 = df.c2.values.astype(str)

pd.Series(
    count(c1, c2[:, None]).sum(1),
    c2
)

han solo       2
r2d2           1
finn           1
the emporer    0
c3po           0
leia organa    1
darth vader    1
dtype: int64

Answer 2

You can pass them as category and using value_counts

df.c1.astype('category',categories=df.c2.tolist()).value_counts(sort=False)
Out[572]: 
han solo       2
r2d2           1
finn           1
the emporer    0
c3po           0
leia organa    1
darth vader    1
Name: c1, dtype: int64

Or you can do

pd.crosstab(df.c2,df.c1).sum().reindex(df.c2,fill_value=0)
Out[592]: 
c2
han solo       2
r2d2           1
finn           1
the emporer    0
c3po           0
leia organa    1
darth vader    1

Answer 3

df[c3] = pd.Series([df[c1].count(n) for n in df[c2]])