how to use sort_index with specific order in pandas

Question

I want to use sort_index to sort value_counts()

The df I have is like this

   a
1 low
2 high
3 vhigh
...

I want to counts columns a and sort them by index of low,med,high,vhigh

df['a'].value_counts()
med   20
high  30
low   10
vhigh 15

If I add sort_index,it will be like this

high  30
low   10
med   20
vhigh 15

That's what I want

low   10
med   20
high  30
vhigh 15

value_counts by default it will be sort by value in descending order. I think your sample output is not correct. provide the actual data frame — Mohamed Thasin ah
– Mohamed Thasin ah, Commented May 9, 2018 at 6:52
I didn't use sort_index at sample, if I add it. the result will be sort in descending, but it still not the answer what am I expecting — Haliris
– Haliris, Commented May 9, 2018 at 6:54

Vivek Kalyanarangan · Accepted Answer · 2020-03-04 13:19:54Z

9

Given the question, this has to be a custom sorting problem -

   value  counts
0    med      20
1   high      30
2    low      10
3  vhigh      15

This is the df you get when you do a value_counts()

Define the value field as a pd.Categorical and define the order -

df['value'] = pd.Categorical(df['value'], ["low", "med", "high", "vhigh"])

Then do a sort -

df.sort_values('value')

Output

   value  counts
2    low      10
0    med      20
1   high      30
3  vhigh      15

edited Mar 4, 2020 at 13:19

answered May 9, 2018 at 6:56

Vivek Kalyanarangan

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3 Comments

Haliris Over a year ago

Thanks, but acually low,med,high,vhigh is the value of one columns

Vivek Kalyanarangan Over a year ago

@Haliris yes, do this to the output of the value_counts() output dataframe

Benjamin Wang Over a year ago

Thanks. This is very useful for my application too. Interestingly, you didn't need to pass ordered=True when using pd.Categorical() for this to work. I wonder why.

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