Reshape of pandas series?

问题:

It looks to me like a bug in pandas.Series.

a = pd.Series([1,2,3,4])
b = a.reshape(2,2)
b

b has type Series but can not be displayed, the last statement gives exception, very lengthy, the last line is "TypeError: %d format: a number is required, not numpy.ndarray". b.shape returns (2,2), which contradicts its type Series. I am guessing perhaps pandas.Series does not implement reshape function and I am calling the version from np.array? Anyone see this error as well? I am at pandas 0.9.1.

回答1:

You can call reshape on the values array of the Series:

In [4]: a.values.reshape(2,2)
Out[4]: 
array([[1, 2],
       [3, 4]], dtype=int64)

I actually think it won't always make sense to apply reshape to a Series (do you ignore the index?), and that you're correct in thinking it's just numpy's reshape:

a.reshape?
Docstring: See numpy.ndarray.reshape

that said, I agree the fact that it let's you try to do this looks like a bug.

回答2:

The reshape function takes the new shape as a tuple rather than as multiple arguments:

In [4]: a.reshape?
Type:       function
String Form:<function reshape at 0x1023d2578>
File:       /Library/Frameworks/EPD64.framework/Versions/7.3/lib/python2.7/site-packages/numpy/core/fromnumeric.py
Definition: numpy.reshape(a, newshape, order='C')
Docstring:
Gives a new shape to an array without changing its data.

Parameters
----------
a : array_like
    Array to be reshaped.
newshape : int or tuple of ints
    The new shape should be compatible with the original shape. If
    an integer, then the result will be a 1-D array of that length.
    One shape dimension can be -1. In this case, the value is inferred
    from the length of the array and remaining dimensions.

Reshape is actually implemented in Series and will return an ndarray:

In [11]: a
Out[11]: 
0    1
1    2
2    3
3    4

In [12]: a.reshape((2, 2))
Out[12]: 
array([[1, 2],
       [3, 4]])

回答3:

you can directly use a.reshape((2,2)) to reshape a Series, but you can not reshape a pandas DataFrame directly, because there is no reshape function for pandas DataFrame, but you can do reshape on numpy ndarray:

1. convert DataFrame to numpy ndarray
2. do reshape
3. convert back

e.g.

a = pd.DataFrame([[1,2,3],[4,5,6]])
b = a.as_matrix().reshape(3,2)
a = pd.DataFrame(b)

回答4:

Just use this below code:

b=a.values.reshape(2,2)

I think it will help you. u can directly use only reshape() function.but it will give future warning