How to get row number in dataframe in Pandas?

Question

How can I get the number of the row in a dataframe that contains a certain value in a certain column using Pandas? For example, I have the following dataframe:

     ClientID  LastName 0    34        Johnson 1    67        Smith 2    53        Brows   

How can I find the number of the row that has 'Smith' in 'LastName' column?

Answer 1

To get all indices that matches 'Smith'

>>> df[df['LastName'] == 'Smith'].index Int64Index([1], dtype='int64') 

or as a numpy array

>>> df[df['LastName'] == 'Smith'].index.to_numpy()  # .values on older versions array([1]) 

or if there is only one and you want the integer, you can subset

>>> df[df['LastName'] == 'Smith'].index[0] 1 

You could use the same boolean expressions with .loc, but it is not needed unless you also want to select a certain column, which is redundant when you only want the row number/index.

Answer 2

df.index[df.LastName == 'Smith'] 

Or

df.query('LastName == "Smith"').index 

Will return all row indices where LastName is Smith

Int64Index([1], dtype='int64')