How to repeat Pandas data frame?

Question

This is my DataFrame that should be repeated for 5 times:

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

I want to 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 smarter way than appending 4 times. Actually the DataFrame I’m working on should be repeated 50 times.

I haven't found anything practical, including those like np.repeat ---- it just doesn't work on a DataFrame.

Could anyone help?

Answer 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

Answer 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).