how to sort pandas dataframe from one column

Question:

I have a data frame like this:

print(df)

        0          1     2
0   354.7      April   4.0
1    55.4     August   8.0
2   176.5   December  12.0
3    95.5   February   2.0
4    85.6    January   1.0
5     152       July   7.0
6   238.7       June   6.0
7   104.8      March   3.0
8   283.5        May   5.0
9   278.8   November  11.0
10  249.6    October  10.0
11  212.7  September   9.0

As you can see, months are not in calendar order. So I created a second column to get the month number corresponding to each month (1-12). From there, how can I sort this data frame according to calendar months’ order?

Asked By: Sachila Ranawaka

||

Answers:

Use sort_values to sort the df by a specific column’s values:

In [18]:
df.sort_values('2')

Out[18]:
        0          1     2
4    85.6    January   1.0
3    95.5   February   2.0
7   104.8      March   3.0
0   354.7      April   4.0
8   283.5        May   5.0
6   238.7       June   6.0
5   152.0       July   7.0
1    55.4     August   8.0
11  212.7  September   9.0
10  249.6    October  10.0
9   278.8   November  11.0
2   176.5   December  12.0

If you want to sort by two columns, pass a list of column labels to sort_values with the column labels ordered according to sort priority. If you use df.sort_values(['2', '0']), the result would be sorted by column 2 then column 0. Granted, this does not really make sense for this example because each value in df['2'] is unique.

Answered By: EdChum

Just adding some more operations on data. Suppose we have a dataframe df, we can do several operations to get desired outputs

ID         cost      tax    label
1       216590      1600    test      
2       523213      1800    test 
3          250      1500    experiment

(df['label'].value_counts().to_frame().reset_index()).sort_values('label', ascending=False)

will give sorted output of labels as a dataframe

    index   label
0   test        2
1   experiment  1
Answered By: Hari_pb

I tried the solutions above and I do not achieve results, so I found a different solution that works for me. The ascending=False is to order the dataframe in descending order, by default it is True. I am using python 3.6.6 and pandas 0.23.4 versions.

final_df = df.sort_values(by=['2'], ascending=False)

You can see more details in pandas documentation here.

Answered By: Joel Carneiro

Just as another solution:

Instead of creating the second column, you can categorize your string data(month name) and sort by that like this:

df.rename(columns={1:'month'},inplace=True)
df['month'] = pd.Categorical(df['month'],categories=['December','November','October','September','August','July','June','May','April','March','February','January'],ordered=True)
df = df.sort_values('month',ascending=False)

It will give you the ordered data by month name as you specified while creating the Categorical object.

Answered By: alireza yazdandoost

Here is template of sort_values according to pandas documentation.

DataFrame.sort_values(by, axis=0,
                          ascending=True,
                          inplace=False,
                          kind='quicksort',
                          na_position='last',
                          ignore_index=False, key=None)[source]

In this case it will be like this.

df.sort_values(by=['2'])

API Reference pandas.DataFrame.sort_values

Answered By: Nafees Ahmad

Using column name worked for me.

sorted_df = df.sort_values(by=['Column_name'], ascending=True)
Answered By: Niraj

This worked for me

df.sort_values(by='Column_name', inplace=True, ascending=False)
Answered By: suzanne chen

Panda’s sort_values does the work.

If one intends to keep the same variable name, don’t forget the inplace=True (this performs the operation in-place)

df.sort_values(by=['2'], inplace=True)

One might as well assign the change (sort) to a variable, that may have the same name, such as the df as

df = df.sort_values(by=['2'])

Forgetting the steps mentioned above may lead one (as this user) to not be able to get the expected result.

Note that if one wants in descending order, one needs to pass ascending=False, such as

df = df.sort_values(by=['2'], ascending=False)
Answered By: Gonçalo Peres

This one worked for me:

df=df.sort_values(by=[2])

Whereas:

df=df.sort_values(by=['2']) 

is not working.

Answered By: Hemapriya R.

Example:
Assume you have a column with values 1 and 0 and you want to separate and use only one value, then:

// furniture is one of the columns in the csv file.
 

allrooms = data.groupby('furniture')['furniture'].agg('count')
allrooms


myrooms1 = pan.DataFrame(allrooms, columns = ['furniture'], index = [1])

myrooms2 = pan.DataFrame(allrooms, columns = ['furniture'], index = [0])

print(myrooms1);print(myrooms2)
Answered By: AeStudios

You probably need to reset the index after sorting:

df = df.sort_values('2')
df = df.reset_index(drop=True)
Answered By: mojtaba rezaei

Just adding a few more insights

df=raw_df['2'].sort_values() # will sort only one column (i.e 2)

but ,

df =raw_df.sort_values(by=["2"] , ascending = False)  # this  will sort the whole df in decending order on the basis of the column "2"
Answered By: Prateek Mohapatra