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Pandas Series: sample() function

Random items from an axis of Pandas object

The sample() function is used to get a random sample of items from an axis of object.

Syntax:

Series.sample(self, n=None, frac=None, replace=False, weights=None, random_state=None, axis=None)
Pandas Series sample image

Parameters:

Name Description Type/Default Value Required / Optional
n Number of items from axis to return. Cannot be used with frac. Default = 1 if frac = None. int optional
frac Fraction of axis items to return. Cannot be used with n. float optional
replace Sample with or without replacement. bool
Default Value: False
Required
weights Default ‘None’ results in equal probability weighting. If passed a Series, will align with target object on index. Index values in weights not found in sampled object will be ignored and index values in sampled object not in weights will be assigned weights of zero. If called on a DataFrame, will accept the name of a column when axis = 0. Unless weights are a Series, weights must be same length as axis being sampled. If weights do not sum to 1, they will be normalized to sum to 1. Missing values in the weights column will be treated as zero. Infinite values not allowed. str or ndarray-like optional
random_state Seed for the random number generator (if int), or numpy RandomState object. int or numpy.random.RandomState, optional
axis Axis to sample. Accepts axis number or name. Default is stat axis for given data type (0 for Series and DataFrames). int or string optional

Returns: Series or DataFrame
A new object of same type as caller containing n items randomly sampled from the caller object.

Example - Generate a DataFrame with default index:

Python-Pandas Code:

import numpy as np
import pandas as pd
df = pd.DataFrame({'num_legs': [2, 4, 8, 0],
                   'num_wings': [2, 0, 0, 0],
                   'num_specimen_seen': [8, 2, 1, 6]},
                  index=['sparrow', 'cat', 'spider', 'snake'])
df

Output:

       num_legs	num_wings	num_specimen_seen
sparrow	    2	    2	     8
cat	        4	    0	     2
spider	    8	    0	     1
snake	       0	    0	     6

Example - Extract 3 random elements from the Series df['num_legs']: Note that we use random_state to ensure the reproducibility of the examples:

Python-Pandas Code:

import numpy as np
import pandas as pd
df = pd.DataFrame({'num_legs': [2, 4, 8, 0],
                   'num_wings': [2, 0, 0, 0],
                   'num_specimen_seen': [8, 2, 1, 6]},
                  index=['sparrow', 'cat', 'spider', 'snake'])
df['num_legs'].sample(n=3, random_state=1)

Output:

snake      0
spider     8
sparrow    2
Name: num_legs, dtype: int64

Example - A random 50% sample of the DataFrame with replacement:

Python-Pandas Code:

import numpy as np
import pandas as pd
df = pd.DataFrame({'num_legs': [2, 4, 8, 0],
                   'num_wings': [2, 0, 0, 0],
                   'num_specimen_seen': [8, 2, 1, 6]},
                  index=['sparrow', 'cat', 'spider', 'snake'])
df.sample(frac=0.5, replace=True, random_state=1)

Output:

              num_legs	num_wings	num_specimen_seen
cat	            4	         0    	    2
snake	        0	         0	        6

Example - Using a DataFrame column as weights. Rows with larger value in the num_specimen_seen column are more likely to be sampled:

Python-Pandas Code:

import numpy as np
import pandas as pd
df = pd.DataFrame({'num_legs': [2, 4, 8, 0],
                   'num_wings': [2, 0, 0, 0],
                   'num_specimen_seen': [8, 2, 1, 6]},
                  index=['sparrow', 'cat', 'spider', 'snake'])
df.sample(n=2, weights='num_specimen_seen', random_state=1)

Output:

                   num_legs	num_wings	num_specimen_seen
sparrow	           2	       2	        8
snake	              0	       0	        6

Previous: Generate a new Pandas series with the index reset
Next: Series-set_axis() function



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