How to filter rows containing a string pattern from a Pandas dataframe

Question

Assume we have a data frame in Python Pandas that looks like this   df   pd DataFrame   vals    1  2  3  4    ids    u aball   u bball   u cnut   u fball       Or  in table form   ids    vals aball   1 bball   2 cnut    3 fball   4   How do I filter rows which contain the key word  ball   For example  the output should be   ids    vals aball   1 bball   2 fball   4

User · Accepted Answer

In  3   df df  ids   str contains  ball    Out 3        ids  vals 0  aball     1 1  bball     2 3  fball     4

User · Answer

df df  ids   str contains  ball   na   False     valid for  at least  pandas version 0 17 1   Step-by-step explanation  from inner to outer     df  ids   selects the ids column of the data frame  technically  the object df  ids   is of type pandas Series  df  ids   str allows us to apply vectorized string methods  e g   lower  contains  to the Series df  ids   str contains  ball   checks each element of the Series as to whether the element value has the string  ball  as a substring  The result is a Series of Booleans indicating True or False about the existence of a  ball  substring  df df  ids   str contains  ball    applies the Boolean  mask  to the dataframe and returns a view containing appropriate records  na   False removes NA   NaN values from consideration  otherwise a ValueError may be returned

User · Answer

gt  gt  gt  mask   df  ids   str contains  ball        gt  gt  gt  mask 0     True 1     True 2    False 3     True Name  ids  dtype  bool   gt  gt  gt  df mask       ids  vals 0  aball     1 1  bball     2 3  fball     4

User · Answer

If you want to set the column you filter on as a new index  you could also consider to use  filter  if you want to keep it as a separate column then str contains is the way to go   Let s say you have   df   pd DataFrame   vals    1  2  3  4  5    ids    u aball   u bball   u cnut   u fball    ballxyz             ids  vals 0    aball     1 1    bball     2 2     cnut     3 3    fball     4 4  ballxyz     5   and your plan is to filter all rows in which ids contains ball AND set ids as new index  you can do  df set index  ids   filter like  ball   axis 0    which gives           vals ids           aball       1 bball       2 fball       4 ballxyz     5   But filter also allows you to pass a regex  so you could also filter only those rows where the column entry ends with ball  In this case you use  df set index  ids   filter regex  ball    axis 0          vals ids         aball     1 bball     2 fball     4   Note that now the entry with ballxyz is not included as it starts with ball and does not end with it   If you want to get all entries that start with ball you can simple use  df set index  ids   filter regex   ball   axis 0    yielding           vals ids           ballxyz     5   The same works with columns  all you then need to change is the axis 0 part  If you filter based on columns  it would be axis 1

[python] How to filter rows containing a string pattern from a Pandas dataframe

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