How to repeat Pandas data frame?

问题

This is my data frame that should be repeated for 5 times:

>>> x = pd.DataFrame({'a':1,'b':2},index = range(1))
>>> x
   a  b
0  1  2

I wanna have the result like this:

>>> x.append(x).append(x).append(x)
   a  b
0  1  2
0  1  2
0  1  2
0  1  2

But there must be a way smarter than keep appending.. Actually the data frame Im working on should be repeated for 50 times..

I haven't found anything practical, including those like np.repeat ---- it just doesnt work on data frame.

Could anyone help?

回答1:

You can use the concat function:

In [13]: pd.concat([x]*5)
Out[13]: 
   a  b
0  1  2
0  1  2
0  1  2
0  1  2
0  1  2

If you only want to repeat the values and not the index, you can do:

In [14]: pd.concat([x]*5, ignore_index=True)
Out[14]: 
   a  b
0  1  2
1  1  2
2  1  2
3  1  2
4  1  2

回答2:

I think it's cleaner/faster to use iloc nowadays:

In [11]: np.full(3, 0)
Out[11]: array([0, 0, 0])

In [12]: x.iloc[np.full(3, 0)]
Out[12]:
   a  b
0  1  2
0  1  2
0  1  2

More generally, you can use tile or repeat with arange:

In [21]: df = pd.DataFrame([[1, 2], [3, 4]], columns=["A", "B"])

In [22]: df
Out[22]:
   A  B
0  1  2
1  3  4

In [23]: np.tile(np.arange(len(df)), 3)
Out[23]: array([0, 1, 0, 1, 0, 1])

In [24]: np.repeat(np.arange(len(df)), 3)
Out[24]: array([0, 0, 0, 1, 1, 1])

In [25]: df.iloc[np.tile(np.arange(len(df)), 3)]
Out[25]:
   A  B
0  1  2
1  3  4
0  1  2
1  3  4
0  1  2
1  3  4

In [26]: df.iloc[np.repeat(np.arange(len(df)), 3)]
Out[26]:
   A  B
0  1  2
0  1  2
0  1  2
1  3  4
1  3  4
1  3  4

Note: This will work with non-integer indexed DataFrames (and Series).

回答3:

I would generally not repeat and/or append, unless your problem really makes it necessary - it is highly inefficiently and typically comes from not understanding the proper way to attack a problem.

I don't know your exact use case, but if you have your values stored as

values = array(1, 2)
df2 = pd.DataFrame(index=arange(0,50),  columns=['a', 'b'])
df2[['a', 'b']] = values

will do the job. Perhaps you want to better explain what you're trying to achieve?

回答4:

Append should work too:

In [589]: x = pd.DataFrame({'a':1,'b':2},index = range(1))

In [590]: x
Out[590]: 
   a  b
0  1  2

In [591]: x.append([x]*5, ignore_index=True) #Ignores the index as per your need
Out[591]: 
   a  b
0  1  2
1  1  2
2  1  2
3  1  2
4  1  2
5  1  2

In [592]: x.append([x]*5)
Out[592]: 
   a  b
0  1  2
0  1  2
0  1  2
0  1  2
0  1  2
0  1  2

回答5:

Try using numpy.repeat:

>>> df=pd.DataFrame(pd.np.repeat(x.values,5,axis=0),columns=x.columns)
>>> df
   a  b
0  1  2
1  1  2
2  1  2
3  1  2
4  1  2
>>>

来源：https://stackoverflow.com/questions/23887881/how-to-repeat-pandas-data-frame

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