"如何在 Pandas DataFrame 中移动一列"

Question

I would like to shift a column in a Pandas DataFrame<\/code> , but I haven't been able to find a method to do it from the documentation without rewriting the whole DF. Does anyone know how to do it? DataFrame:

##    x1   x2
##0  206  214
##1  226  234
##2  245  253
##3  265  272
##4  283  291

Answer 1

In [18]: a
Out[18]: 
   x1  x2
0   0   5
1   1   6
2   2   7
3   3   8
4   4   9

In [19]: a['x2'] = a.x2.shift(1)

In [20]: a
Out[20]: 
   x1  x2
0   0 NaN
1   1   5
2   2   6
3   3   7
4   4   8

Answer 2

You need to use df.shift here.
df.shift(i) shifts the entire dataframe by i units down.

So, for i = 1 :

Input:

    x1   x2  
0  206  214  
1  226  234  
2  245  253  
3  265  272    
4  283  291

Output:

    x1   x2
0  Nan  Nan   
1  206  214  
2  226  234  
3  245  253  
4  265  272 

So, run this script to get the expected output:

import pandas as pd

df = pd.DataFrame({'x1': ['206', '226', '245',' 265', '283'],
                   'x2': ['214', '234', '253', '272', '291']})

print(df)
df['x2'] = df['x2'].shift(1)
print(df)

Answer 3

Lets define the dataframe from your example by

>>> df = pd.DataFrame([[206, 214], [226, 234], [245, 253], [265, 272], [283, 291]], 
    columns=[1, 2])
>>> df
     1    2
0  206  214
1  226  234
2  245  253
3  265  272
4  283  291

Then you could manipulate the index of the second column by

>>> df[2].index = df[2].index+1

and finally re-combine the single columns

>>> pd.concat([df[1], df[2]], axis=1)
       1      2
0  206.0    NaN
1  226.0  214.0
2  245.0  234.0
3  265.0  253.0
4  283.0  272.0
5    NaN  291.0

Perhaps not fast but simple to read. Consider setting variables for the column names and the actual shift required.

Edit: Generally shifting is possible by df[2].shift(1) as already posted however would that cut-off the carryover.

Answer 4

If you don't want to lose the columns you shift past the end of your dataframe, simply append the required number first:

    offset = 5
    DF = DF.append([np.nan for x in range(offset)])
    DF = DF.shift(periods=offset)
    DF = DF.reset_index() #Only works if sequential index

Answer 5

I suppose imports

import pandas as pd
import numpy as np

First append new row with NaN, NaN,... at the end of DataFrame ( df ).

s1 = df.iloc[0]    # copy 1st row to a new Series s1
s1[:] = np.NaN     # set all values to NaN
df2 = df.append(s1, ignore_index=True)  # add s1 to the end of df

It will create new DF df2. Maybe there is more elegant way but this works.

Now you can shift it:

df2.x2 = df2.x2.shift(1)  # shift what you want

Answer 6

Trying to answer a personal problem and similar to yours I found on Pandas Doc what I think would answer this question:

DataFrame.shift (periods=1, freq=None, axis=0) Shift index by desired number of periods with an optional time freq

Notes

If freq is specified then the index values are shifted but the data is not realigned. That is, use freq if you would like to extend the index when shifting and preserve the original data.

Hope to help future questions in this matter.

Answer 7

df3

    1   108.210 108.231
2   108.231 108.156
3   108.156 108.196
4   108.196 108.074
... ... ...
2495    108.351 108.279
2496    108.279 108.669
2497    108.669 108.687
2498    108.687 108.915
2499    108.915 108.852

df3['yo'] = df3['yo'].shift(-1)

    yo  price
0   108.231 108.210
1   108.156 108.231
2   108.196 108.156
3   108.074 108.196
4   108.104 108.074
... ... ...
2495    108.669 108.279
2496    108.687 108.669
2497    108.915 108.687
2498    108.852 108.915
2499    NaN 108.852

Answer 8

This is how I do it:

df_ext = pd.DataFrame(index=pd.date_range(df.index[-1], periods=8, closed='right'))
df2 = pd.concat([df, df_ext], axis=0, sort=True)
df2["forecast"] = df2["some column"].shift(7)

Basically I am generating an empty dataframe with the desired index and then just concatenate them together. But I would really like to see this as a standard feature in pandas so I have proposed an enhancement to pandas.

Answer 9

I'm new to pandas, and I may not be understanding the question, but this solution worked for my problem:

# Shift contents of column 'x2' down 1 row
df['x2'] = df['x2'].shift()

Or, to create a new column with contents of 'x2' shifted down 1 row

# Create new column with contents of 'x2'  shifted down 1 row
df['x3'] = df['x2'].shift()

I had a read of the official docs for shift() while trying to figure this out, but it doesn't make much sense to me, and has no examples referencing this specific behavior.

Note that the last row of column 'x2' is effectively pushed off the end of the Dataframe. I expected shift() to have a flag to change this behaviour, but I can't find anything.