pd.concat()
pd.concat([df1,df2])
|
Stacks df1 and df2 |
pd.concat([df1,df2],keys=['1','2'])
|
Creates a label (key) for each df |
pd.concat([df1,df2], join='inner')
|
Default join is "inner join" |
df1.append(df2)
|
Does the same thing as pd.concat() |
Multi-indexing
pd.MultiIndex.from_arrays([['a','a','b','b'],[1,2,1,2]])
|
pd.MultiIndex.from_tuples([('a',1),('a',2),('b',1),('b',2)])
|
pd.MultiIndex.from_product([['a','b'],[1,2]])
|
df.sort_index()
|
Orders index in ascending order |
df.reset_index(name='')
|
Turn the index labels into cols |
All three methods of pd.MultiIndex give:
MultiIndex(
[('a', 1),('a', 2),('b', 1),('b', 2)]
)`
|
|
Joins
pd.merge(df1,df2)
|
pd.merge(df1,df2,left_on="a",right_on="b")
|
Merges data using "a" and "b" as keys |
pd.merge(df1,df2,how='inner')
|
Default is "outer join" |
pd.merge(df1,df2, on="a",suffixes=["_L","_R"])
|
When multiple cols have same index and name, gives suffix "_L" and "_R" |
Aggregation and Grouping
df.mean(axis='columns')
|
Calculates the mean across cols |
df.groupby('key').sum()
|
Gives sum for each key |
df.groupby('key')['a'].sum()
|
Gives sum for all rows in col "a" |
df.groupby('key')['a'].describe()
|
Gives summary stats |
df.groupby('key').transform(lambda x:x-x.mean())
|
Applies lambda function as aggregation function |
df.groupby('key').apply(function)
|
Applies "function" as aggregation function |
|
|
Pivot Tables
df.pivot_table(index='a',columns='col',aggfunc='sum')
|
Groups by index and gives the sum of column "a" |
df.pivot_table(index='a',columns='col',aggfunc='sum').plot()
|
Plots values using "a" as x-axis and sum(col) as y-axis |
Pivot tables do the same thing as using groupby with aggregation functions. The main difference is that they are a cleaner way of using multiple aggregation functions at once for a single grouping
|
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