根据 R 中的条件扩展矩阵

Question

考虑以下随机矩阵：

m <- cbind(c("r1","r2","r3","r4","r1","r2","r3","r4"),c(3,2,5,2,5,2,6,4))

我想根据条件扩展它。例如，如何在每行下使用单元格“r4”创建一个额外的行，其中的值与单元格“r4”的行中的值完全相同。因此，我将得到以下矩阵：

m <- cbind(c("r1","r2","r3","r4","r4","r1","r2","r3","r4","r4"),c(3,2,5,2,2,5,2,6,4,4))

Answer 1

您可以使用rep 复制单元格r4 喜欢的每一行：

m[rep(seq_len(nrow(m)), 1 + (m[,1] == "r4")),]
#      [,1] [,2]
# [1,] "r1" "3" 
# [2,] "r2" "2" 
# [3,] "r3" "5" 
# [4,] "r4" "2" 
# [5,] "r4" "2" 
# [6,] "r1" "5" 
# [7,] "r2" "2" 
# [8,] "r3" "6" 
# [9,] "r4" "4" 
#[10,] "r4" "4" 

m[,1] == "r4" 给出一个逻辑向量，你可以在其中加 1 来告诉rep 这行应该给出多少次。