使用R将矩阵划分为N个相等大小的块

Question

如何用R将矩阵或数据帧划分为N个大小相等的块？我想水平切割矩阵或数据框.

例如,给定:

r = 8
c = 10
number_of_chunks = 4
data = matrix(seq(r*c), nrow = r, ncol=c)
>>> data

     [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,]    1    9   17   25   33   41   49   57   65    73
[2,]    2   10   18   26   34   42   50   58   66    74
[3,]    3   11   19   27   35   43   51   59   67    75
[4,]    4   12   20   28   36   44   52   60   68    76
[5,]    5   13   21   29   37   45   53   61   69    77
[6,]    6   14   22   30   38   46   54   62   70    78
[7,]    7   15   23   31   39   47   55   63   71    79
[8,]    8   16   24   32   40   48   56   64   72    80

我想要切入data4个元素的列表:

要素1:

     [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,]    1    9   17   25   33   41   49   57   65    73
[2,]    2   10   18   26   34   42   50   58   66    74

要素2:

     [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[3,]    3   11   19   27   35   43   51   59   67    75
[4,]    4   12   20   28   36   44   52   60   68    76

要素3:

     [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[5,]    5   13   21   29   37   45   53   61   69    77
[6,]    6   14   22   30   38   46   54   62   70    78

要素4:

     [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[7,]    7   15   23   31   39   47   55   63   71    79
[8,]    8   16   24   32   40   48   56   64   72    80

在python中使用numpy,我可以使用numpy.array_split.

Answer 1

这是基础R的尝试.使用计算行序列的"漂亮"剪切值pretty.将行号序列分类cut并返回切割值处的序列分组列表split.最后,使用lapply提取矩阵子集来运行拆分行值的列表[.

lapply(split(seq_len(nrow(data)),
             cut(seq_len(nrow(data)), pretty(seq_len(nrow(data)), number_of_chunks))),
       function(x) data[x, ])
$`(0,2]`
     [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,]    1    9   17   25   33   41   49   57   65    73
[2,]    2   10   18   26   34   42   50   58   66    74

$`(2,4]`
     [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,]    3   11   19   27   35   43   51   59   67    75
[2,]    4   12   20   28   36   44   52   60   68    76

$`(4,6]`
     [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,]    5   13   21   29   37   45   53   61   69    77
[2,]    6   14   22   30   38   46   54   62   70    78

$`(6,8]`
     [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,]    7   15   23   31   39   47   55   63   71    79
[2,]    8   16   24   32   40   48   56   64   72    80

将其转换为函数:

array_split <- function(data, number_of_chunks) {
  rowIdx <- seq_len(nrow(data))    
  lapply(split(rowIdx, cut(rowIdx, pretty(rowIdx, number_of_chunks))), function(x) data[x, ])
}

然后,你可以使用

array_split(data=data, number_of_chunks=number_of_chunks)

返回与上面相同的结果.

@ user20650建议的一个很好的简化是

split.data.frame(data,
                 cut(seq_len(nrow(data)), pretty(seq_len(nrow(data)), number_of_chunks)))

令我惊讶的是,split.data.frame当第一个参数是矩阵时,返回矩阵列表.