Convert categorical data in pandas dataframe

Question

I have a dataframe with this type of data  too many columns    col1        int64 col2        int64 col3        category col4        category col5        category   Columns seems like this   Name  col3  dtype  category Categories  8  object    B  C  E  G  H  N  S  W    I want to convert all value in columns to integer like this    1  2  3  4  5  6  7  8    I solved this for one column by this   dataframe  c     pandas Categorical from array dataframe col3  codes   Now I have two columns in my dataframe - old col3 and new c and need to drop old columns    That s bad practice  It s work but in my dataframe many columns and I don t want do it manually     How do this pythonic and just cleverly

User · Answer

For a certain column  if you don t care about the ordering  use this  df  col1 num     df  col1   apply lambda x  np where df  col1   unique    x  0  0     If you care about the ordering  specify them as a list and use this  df  col1 num     df  col1   apply lambda x    first    second    third   index x

User · Answer

First  to convert a Categorical column to its numerical codes  you can do this easier with  dataframe  c   cat codes  Further  it is possible to select automatically all columns with a certain dtype in a dataframe using select dtypes  This way  you can apply above operation on multiple and automatically selected columns   First making an example dataframe   In  75   df   pd DataFrame   col1   1 2 3 4 5    col2  list  abcab      col3  list  ababb      In  76   df  col2     df  col2   astype  category    In  77   df  col3     df  col3   astype  category    In  78   df dtypes Out 78   col1       int64 col2    category col3    category dtype  object   Then by using select dtypes to select the columns  and then applying  cat codes on each of these columns  you can get the following result   In  80   cat columns   df select dtypes   category    columns  In  81   cat columns Out 81   Index  u col2   u col3    dtype  object    In  83   df cat columns    df cat columns  apply lambda x  x cat codes   In  84   df Out 84      col1  col2  col3 0     1     0     0 1     2     1     1 2     3     2     0 3     4     0     1 4     5     1     1

User · Answer

Here multiple columns need to be converted  So  one approach i used is     for col name in df columns      if df col name  dtype     object            df col name   df col name  astype  category           df col name    df col name  cat codes   This converts all string   object type columns to categorical  Then applies codes to each type of category

User · Answer

This works for me   pandas factorize    B    C    D    B     0    Output    0  1  2  0

User · Answer

Answers here seem outdated  Pandas now has a factorize   function and you can create categories as  df col factorize     Function signature  pandas factorize values  sort False  na sentinel - 1  size hint None

User · Answer

For converting categorical data in column C of dataset data  we need to do the following   from sklearn preprocessing import LabelEncoder  labelencoder  LabelEncoder    initializing an object of class LabelEncoder data  C     labelencoder fit transform data  C     fitting and transforming the desired categorical column

User · Answer

If your concern was only that you making a extra column and deleting it later  just dun use a new column at the first place   dataframe   pd DataFrame   col1   1 2 3 4 5    col2  list  abcab      col3  list  ababb     dataframe col3   pd Categorical from array dataframe col3  codes   You are done  Now as Categorical from array is deprecated  use Categorical directly  dataframe col3   pd Categorical dataframe col3  codes   If you also need the mapping back from index to label  there is even better way for the same  dataframe col3  mapping index   pd Series dataframe col3  factorize     check below   print dataframe  print mapping index get loc  c

User · Answer

What I do is  I replace values  Like this- df  col   replace to replace   category 1    category 2    category 3    value  1  2  3   inplace True   In this way  if the col column has categorical values  they get replaced by the numerical values

User · Answer

You can do it less code like below   f   pd DataFrame   col1   1 2 3 4 5    col2  list  abcab    col3  list  ababb      f  col1    f  col1   astype  category   cat codes f  col2    f  col2   astype  category   cat codes f  col3    f  col3   astype  category   cat codes  f

User · Answer

Quickbeam2k1  see below                            -  dataset pd read csv  Data2 csv   np set printoptions threshold np nan  X   dataset iloc      values   Using sklearn   from sklearn preprocessing import LabelEncoder labelencoder X LabelEncoder   X   0    labelencoder X fit transform X   0

User · Answer

One of the simplest ways to convert the categorical variable into dummy indicator variables is to use get dummies provided by pandas  Say for example we have data in which sex is a categorical value  male  amp  female  and you need to convert it into a dummy indicator here is how to do it   x000D   x000D  tranning data   pd read csv     titanic train csv   features     Age    Sex       here sex is catagorical value X train   pd get dummies tranning data features   print X train   Age Sex female Sex male 20    0          1 33    1          0 40    1          0 22    1          0 54    0          1 x000D   x000D   x000D

[python] Convert categorical data in pandas dataframe

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