Print the value of a column in a dataframe that is not contained in another dataframe

Question

I have two dataframes:

df1 = pd.DataFrame({'System':['b0001','b0002']})
df2 = pd.DataFrame({'System':['b0001']})

I want to print the value in column System of df1 that is NOT contained in column System of df2. The output should only be:

b0002

My current code is:

for i in df1.index:
    if df1.System[i] not in df2.System:
        print (df1.System[i])

But the output is:

b0001 
b0002

I cant'f figure out why it still prints out b0001. I've tried with isin and the output is the same.

Any help will be appreciated.

Answer 1

A pandas way of doing this is to use isin as follows:

df1[~df1.System.isin(df2.System)]

Output:

  System
1  b0002

However, to do it the way you are doing you are missing .values:

for i in df1.index:
    if df1.System[i] not in df2.System.values:
        print (df1.System[i])

Output:

b0002

Answer 2

numpy

np.setdiff1d(df1.System.values, df2.System.values)

array(['b0002'], dtype=object)