pandas select based on column from another dataframe code example

Example 1: only keep rows of a dataframe based on a column value

df.loc[df['column_name'] == some_value]

Example 2: how to pick out separate columns from the pandas dataframe object

df1 = df.iloc[:, 0:2] # If you want to do it by index. Remember that Python does not slice inclusive of the ending index.
df1 = df[['a', 'b']] ## if you want to do it b nae