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pandas_groupby [2021/07/06 23:02] – [preserve the highest odd value in each group] adminpandas_groupby [2024/03/26 22:25] – [groupby slicing] raju
Line 77: Line 77:
  
 ==== preserve the highest odd value in each group ==== ==== preserve the highest odd value in each group ====
 +tags | pandas groupby transform maximum odd number, maxodd
 +
 Given Given
 <code> <code>
Line 93: Line 95:
 11  MM7  S7     t      3 11  MM7  S7     t      3
 </code> </code>
-get all the rows with highest odd 'count' for each ['Sp', 'Mt'] combination. That is, we want+ 
 +We want
 <code> <code>
      Sp  Mt Value  count      Sp  Mt Value  count
Line 103: Line 106:
 11  MM7  S7     t      3 11  MM7  S7     t      3
 </code> </code>
 +That is get all the rows with highest odd 'count' for each ['Sp', 'Mt'] combination.
 +If there is a group with only even 'count' values, discard it.
 +
 Solution Solution
 <code> <code>
Line 169: Line 175:
  
 In [5]: In [5]:
-df.groupby(['Sp', 'Mt'])['count'].transform(max_odd) == df['count']+idx = df.groupby(['Sp', 'Mt'])['count'].transform(max_odd) == df['count'] 
 +idx
 Out[5]: Out[5]:
 0     False 0     False
Line 230: Line 237:
  
 ==== extract groupby object by key ==== ==== extract groupby object by key ====
 +tags | pandas groupby filter a group
 +
   * groups.get_group(key_value) if grouping on a single column   * groups.get_group(key_value) if grouping on a single column
   * groups.get_group(key_value_tuple) if grouping on multiple columns.   * groups.get_group(key_value_tuple) if grouping on multiple columns.
Line 310: Line 319:
 5  bar  0  6 5  bar  0  6
 </code> </code>
 +
 +==== groupby slicing ====
 +Consider
 +<code>
 +In [1]: 
 +import pandas as pd
 +import numpy as np
 +rand = np.random.RandomState(1)
 +df = pd.DataFrame({'A': ['foo', 'bar'] * 3,
 +                   'B': rand.randn(6),
 +                   'C': rand.randint(0, 20, 6)})
 +
 +In [2]: 
 +df
 +Out[2]: 
 +     A         B   C
 +0  foo  1.624345   5
 +1  bar -0.611756  18
 +2  foo -0.528172  11
 +3  bar -1.072969  10
 +4  foo  0.865408  14
 +5  bar -2.301539  18
 +</code>
 +
 +Group by on column 'A'
 +<code>
 +In [3]: 
 +gb = df.groupby(['A'])
 +</code>
 +
 +You can use get_group() to get a single group
 +<code>
 +In [4]: 
 +gb.get_group('foo')
 +Out[4]: 
 +     A         B   C
 +0  foo  1.624345   5
 +2  foo -0.528172  11
 +4  foo  0.865408  14
 +</code>
 +
 +You can select different columns using the groupby slicing:
 +<code>
 +In [5]: 
 +gb[['A', 'B']].get_group('foo')
 +Out[5]: 
 +     A         B
 +0  foo  1.624345
 +2  foo -0.528172
 +4  foo  0.865408
 +
 +In [6]: 
 +gb[['C']].get_group('foo')
 +Out[6]: 
 +    C
 +0   5
 +2  11
 +4  14
 +</code>
 +
 +Ref:
 +  * https://stackoverflow.com/questions/14734533/how-to-access-subdataframes-of-pandas-groupby-by-key
  
 ==== apply a function on each group ==== ==== apply a function on each group ====
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 tags | reset_index remove level_1 column, apply function to multiple columns and rename result, groupby apply name the result, groupby apply remove level_1 tags | reset_index remove level_1 column, apply function to multiple columns and rename result, groupby apply name the result, groupby apply remove level_1
- 
  
pandas_groupby.txt · Last modified: 2024/05/07 20:47 by raju