Python pandas: How many values of one series are in another?

Question

I have two pandas dataframes:

df1 = pd.DataFrame(
    {
    "col1": ["1","2",np.nan,"3"],
    }
)

df2 = pd.DataFrame(
    {
    "col1": [2.0,3.0,4.0,np.nan],
    }
)

I would like to know how many values of df1.col1 exist in df2.col1. In this case it should be 2 as I want "2" and 2.0 to be seen as equal.

I do have a working solution, but because I think I'll need this more often (and for learning purposes, of cause), I wanted to ask you if there is a more comfortable way to do that.

df1.col1[df1.col1.notnull()].isin(df2.col1[df2.col1.notnull()].astype(int).astype(str)).value_counts()

Answer 1

Use Series.dropna and convert to floats, if working with integers and missing values:

a = df1.col1.dropna().astype(float).isin(df2.col1.dropna()).value_counts()

Or:

a = df1.col1.dropna().isin(df2.col1.dropna().astype(int).astype(str)).value_counts()