Suppose I have a dataframe with columns a, b and c, I want to sort the dataframe by column b in ascending order, and by column c in descending order, how do I do this?
In[11]: df1 = pd.DataFrame(np.random.randint(1,5,(10,2)), columns=['a','b'])In[12]: df1.sort(['a','b'], ascending=[True,False])Out[12]:
a b
214713112312432644043943541841
As of the 0.17.0 release, the sort method was deprecated in favor of sort_values. sort was completely removed in the 0.20.0 release. The arguments (and results) remain the same:
As of pandas 0.17.0, DataFrame.sort() is deprecated, and set to be removed in a future version of pandas. The way to sort a dataframe by its values is now is DataFrame.sort_values
For large dataframes of numeric data, you may see a significant performance improvement via numpy.lexsort, which performs an indirect sort using a sequence of keys:
import pandas as pd
import numpy as np
np.random.seed(0)
df1 = pd.DataFrame(np.random.randint(1, 5, (10,2)), columns=['a','b'])
df1 = pd.concat([df1]*100000)
def pdsort(df1):
return df1.sort_values(['a', 'b'], ascending=[True, False])
def lex(df1):
arr = df1.values
return pd.DataFrame(arr[np.lexsort((-arr[:, 1], arr[:, 0]))])
assert (pdsort(df1).values == lex(df1).values).all()
%timeit pdsort(df1) # 193 ms per loop
%timeit lex(df1) # 143 ms per loop
One peculiarity is that the defined sorting order with numpy.lexsort is reversed: (-'b', 'a') sorts by series a first. We negate series b to reflect we want this series in descending order.
Be aware that np.lexsort only sorts with numeric values, while pd.DataFrame.sort_values works with either string or numeric values. Using np.lexsort with strings will give: TypeError: bad operand type for unary -: 'str'.
