Question

几乎每天都有人再次对我进行指控:

m <- matrix( 1:6, ncol=2 )
while( dim(m)[1] > 0 ){
  print(m);
  m <- m[-1,]
}

gives:

     [,1] [,2]
[1,]    1    4
[2,]    2    5
[3,]    3    6
     [,1] [,2]
[1,]    2    5
[2,]    3    6
Error in while (dim(m)[1] > 0) { : argument is of length zero

R是否与1xn matrices有问题,或我的错误在哪里?

> nrow( m[-c(2,3), ] )
NULL
> dim( m[-c(2,3), ] )
NULL
> m[-c(2,3), ][,1]
Error in m[-c(2, 3), ][, 1] : incorrect number of dimensions
> str( m[-c(2,3), ] )
int [1:2] 1 4

Any idea how to easily fix the initial example, which is close to my actual problem? BTW: This loop is the bottleneck of my algorithm. Hence, efficient solutions are appreciated.

感谢!

Answer 1

<代码>()的缺省行为是指酌情转换成更简单的结构。换言之,一旦你排入1xn矩阵,该物体就会变成病媒。

为改变这种行为,请使用<代码>drop=FALSE的论点至[:

m <- matrix( 1:6, ncol=2 )
while( dim(m)[1] > 0 ){
  print(m);
  m <- m[-1, , drop=FALSE]
}

     [,1] [,2]
[1,]    1    4
[2,]    2    5
[3,]    3    6
     [,1] [,2]
[1,]    2    5
[2,]    3    6
     [,1] [,2]
[1,]    3    6

详情见?”

友情链接