问题
I have a dataframe and I am looking at one column within the dataframe called names
array(['Katherine', 'Robert', 'Anne', nan, 'Susan', 'other'], dtype=object)
I am trying to make a call to tell me how many times each of these unique names shows up in the column, for example if there are 223 instances of Katherine etc. How do i do this? i know value_counts just shows 1 for each of these because they are the separate unique values
回答1:
If I understand you correctly, you can use pandas.Series.value_counts.
Example:
import pandas as pd
import numpy as np
s = pd.Series(['Katherine', 'Robert', 'Anne', np.nan, 'Susan', 'other'])
s.value_counts()
Katherine 1
Robert 1
other 1
Anne 1
Susan 1
dtype: int64
The data you provided only has one of each name - so here is an example with multiple 'Katherine' entries:
s = pd.Series(['Katherine','Katherine','Katherine','Katherine', 'Robert', 'Anne', np.nan, 'Susan', 'other'])
s.value_counts()
Katherine 4
Robert 1
other 1
Anne 1
Susan 1
dtype: int64
When applied to your Dataframe you will call this as follows:
df['names'].value_counts()
回答2:
You could use group by to achieve that:
df[['col1']].groupby(['col1']).agg(['count'])
来源：https://stackoverflow.com/questions/41665659/count-of-unique-value-in-column-pandas