使用R中的条件减少列数

Question

我有一个超过1000行和100列的大矩阵.在每行中只有6-10列具有值,其余为零.我想创建一个只有5列的矩阵,它取每行中5个连续列的值.例如:

A = structure(c(0, 1L, 6L, 0, 2L, 0, 2L, 0, 1L, 4L, 1L, 3L, 7L, 2L, 6L, 2L, 4L, 0, 3L, 0, 3L, 5L, 1L, 4L, 0, 4L, 6L, 2L, 0, 0, 5L, 0, 3L, 5L, 0, 0, 0, 4L, 6L, 7L, 0, 7L, 5L, 7L, 8L, 6L, 0, 0, 8L, 9L, 0, 0, 0, 9L, 1L, 0 , 0, 0, 0, 2L, 7L, 0, 2L, 0, 0, 1L, 8L, 4, 0, 0), .Dim = c(5L, 14L))

#A =
#     [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12] [,13] [,14]
#[1,]    0    0    1    2    3    4    5    0    0     6     0     0     7     1
#[2,]    1    2    3    4    5    6    0    0    7     0     0     0     0     8
#[3,]    6    0    7    0    1    2    3    4    5     0     0     0     2     4
#[4,]    0    1    2    3    4    0    5    6    7     8     9     0     0     0
#[5,]    2    4    6    0    0    0    0    7    8     9     1     2     0     0

我想要这个矩阵:

B = structure(c(1L, 1L, 1L, 5L, 7L, 2L, 2L, 2L, 6L, 8L, 3L, 3L, 3L, 7L, 9L, 4L, 4L, 4L, 8L, 1L, 5L, 5L, 5L, 9L, 2L), .Dim = c(5L, 5L))


#B = 
#     [,1] [,2] [,3] [,4] [,5]
#[1,]    1    2    3    4    5
#[2,]    1    2    3    4    5
#[3,]    1    2    3    4    5
#[4,]    5    6    7    8    9
#[5,]    7    8    9    1    2

我的代码:

df = data.frame(A)
B = do.call(rbind, lapply(1:NROW(df), function(i) df[i,][(df[i,])!=0][1:5]))
# or
B = t(apply(X = df, MARGIN = 1, function(x) x[x!=0][1:5]))

我的代码适用于A的前两行,但其余行则无效.我还考虑过获取无零的列索引,然后查看是否有5个连续的列(它们之间没有任何间隙)并检索它们的值.任何帮助非常感谢!

Answer 1

您可以使用rollapply：

library(zoo)
t(apply(A,1,function(x) {x[match(T,rollapply(!!x,5,all)) + (0:4)]}))

#      [,1] [,2] [,3] [,4] [,5]
# [1,]    1    2    3    4    5
# [2,]    1    2    3    4    5
# [3,]    1    2    3    4    5
# [4,]    5    6    7    8    9
# [5,]    7    8    9    1    2

如果您的行没有任何 5 的序列，它将崩溃，如果您希望处理它，请更新您的帖子。

或者相同但更漂亮：

library(purrr)
Adf       <- as.data.frame(t(A)) # data.frame fits more this data conceptually, you have different series, and it's better to put them in columns
res_df  <- map_df(Adf,~ {.x[match(T,rollapply(.x!=0,5,all))+(0:4)]})
res_mat <- as.matrix(t(unname(res_df))) # if you want to go back to ugly :)