使用numpy pandas 进行矩阵运算 [英] matrix operation using numpy pandas

问题描述

我正在尝试测试使用numpy和熊猫

在3.5.0-17-generic #28-Ubuntu SMP Tue Oct 9 19:32:08 UTC 2012 i686 i686 i686 GNU/Linux上与python 2.7.3, numpy 1.9.2 and pandas 0.15.2

对于这个小例子:

ds1 = [[ 4, 13,  6,  9],
       [ 7, 12,  5,  7],
       [ 7,  0,  4, 22],
       [ 9,  8, 12,  0]]
ds2 = [[ 4,  1],
       [ 5,  3],
       [ 6,  1],
       [ 7,  2],
       [ 8,  2],
       [ 9,  3],
       [12,  1],
       [13,  2],
       [22,  3]]

ds1= pd.DataFrame(ds1)
ds2= pd.DataFrame(ds2)
C = np.where(ds1.values.ravel()[:, None] == ds2.values[:, 0])
print C

给出错误的结果

(array([ 0,  1,  2,  3,  4,  5,  6,  7,  8, 10, 11, 12, 13, 14]), 
 array([ 0, 7, 2, 5, 3, 6, 1, 3, 3, 0, 8, 5, 4, 6]))

预期输出为

output = [[1, 2, 1, 3],
          [2, 1, 3, 2],
          [2, 0, 1, 3],
          [3, 2, 1, 0]]

并且在处理较大的矩阵值时

and while working with large matrix values

ds1 = pd.read_table('https://gist.githubusercontent.com/karimkhanp/9527bad750fbe75e072c/raw/ds1', sep=' ', header=None)
ds2 = pd.read_table('https://gist.githubusercontent.com/karimkhanp/1692f1f76718c35e939f/raw/6f6b348ab0879b702e1c3c5e362e9d2062e9e9bc/ds2', header=None, sep=' ')
C = np.where(ds1.values.ravel()[:, None] == ds2.values[:, 0])
print C

给出

(1000, 1001) (4000, 2)
(array([], dtype=int32),)

而不是替换后的矩阵值.

instead of the replaced matrix value.

任何建议都会很有帮助.

Any suggestion would be much helpful.

推荐答案

我同意@Anthony Lethuillier的回答，我只是猜测IndexError可能是由不同版本引起的.似乎是@nlper的情况，C是(array([], dtype=int32),)，这意味着在ds1.values.ravel()[:, None] == ds2.values[:, 0]中什么都没有发现，这显然与@Anthony的不同.找不到任何内容，因此C是仅包含1个元素的元组，因此在访问C[1]时会触发IndexError.

I agree with @Anthony Lethuillier 's answer and I just guess the IndexError may be caused by different version. It seem's in @nlper 's situation, C is (array([], dtype=int32),) which means nothing found in ds1.values.ravel()[:, None] == ds2.values[:, 0], and this is obviously different from @Anthony 's. Nothing found, thus C is a tuple which only contains 1 element, so an IndexError is triggered when you accessing C[1].

这在我的机器上也可以使用，所以我不知道为什么C为空.我建议您详细打印ds1.values.ravel()和ds2.values[:, 0]并查看为什么没有相等的内容.

This also works on my machine so I don't know why C is empty. I recommend you to print ds1.values.ravel() and ds2.values[:, 0] in detail and see why nothing equals.

此外，我使用python 2.7.9，numpy 1.9.2和pandas 0.16.1

Besides, I use python 2.7.9, numpy 1.9.2 and pandas 0.16.1

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