python - Combining rows in pandas

Question

(This question already has an answer here): question from:https://stackoverflow.com/questions/17438906/combining-rows-in-pandas

Answer 1

Starting from

>>> df
              val1  val2  val3
city_id                       
houston,tx       1     2     0
houston,tx       0     0     1
houston,tx       2     1     1
somewhere,ew     4     3     7

I might do

>>> df.groupby(df.index).sum()
              val1  val2  val3
city_id                       
houston,tx       3     3     2
somewhere,ew     4     3     7

or

>>> df.reset_index().groupby("city_id").sum()
              val1  val2  val3
city_id                       
houston,tx       3     3     2
somewhere,ew     4     3     7

The first approach passes the index values (in this case, the city_id values) to groupby and tells it to use those as the group keys, and the second resets the index and then selects the city_id column. See this section of the docs for more examples. Note that there are lots of other methods in the DataFrameGroupBy objects, too:

>>> df.groupby(df.index)
<pandas.core.groupby.DataFrameGroupBy object at 0x1045a1790>
>>> df.groupby(df.index).max()
              val1  val2  val3
city_id                       
houston,tx       2     2     1
somewhere,ew     4     3     7
>>> df.groupby(df.index).mean()
              val1  val2      val3
city_id                           
houston,tx       1     1  0.666667
somewhere,ew     4     3  7.000000