如何使用for循环在R中创建简单表？

Question

I was asked to create a table with three columns, A, B and C and eight rows. Column A must go 1, 1, 1, 1, 2, 2, 2, 2. Column B must alternate 1, 2, 1, 2, 1, 2, 1, 2. And column C must go 1, 1, 2, 2, 1, 1, 2, 2. I am able to produce the A column data fine, but don't know how to get B or C. This is the code I have so far:

dataSheet <- matrix(nrow = 0, ncol = 3)  
colnames(dataSheet) <- c('A', 'B', 'C')  
A <- 1 
B <- 1 
C <- 1 

for (A in 1:4){
A=1
dataSheet <- rbind(dataSheet, c(A, B, C)) 
}
for (A in 5:8){
A=2
dataSheet <- rbind(dataSheet, c(A, B, C)) 
}

Answer 1

This seems like a good excuse to get familiar with the rep() function as it easily supports this question, but many more complicated questions if you're clever enough:

dt <- data.frame(A = rep(1:2, each = 4),
                 B = rep(1:2, times = 4),
                 C = rep(1:2, each = 2))
dt
#>   A B C
#> 1 1 1 1
#> 2 1 2 1
#> 3 1 1 2
#> 4 1 2 2
#> 5 2 1 1
#> 6 2 2 1
#> 7 2 1 2
#> 8 2 2 2

^{Created on 2019-01-26 by the reprex package (v0.2.1)}

Answer 2

Simply use R 's vectorization for this task, ie

A <- c(1, 1, 1, 1, 2, 2, 2, 2)
B <- c(1, 2, 1, 2, 1, 2, 1, 2) # or rep(1:2, 4)
C <- c(1, 1, 2, 2, 1, 1, 2, 2)
cbind(A,B,C)

Answer 3

Maybe something along the lines of the following will be acceptable by your professor.

for (i in 1:8){
  A <- if(i <= 4) 1 else 2
  B <- if(i %% 2) 1 else 2
  C <- if(any(i %% 4 == c(0, 1, 4, 5))) 1 else 2
  dataSheet <- rbind(dataSheet, c(A, B, C)) 
}

dataSheet
#     A B C
#[1,] 1 1 1
#[2,] 1 2 2
#[3,] 1 1 2
#[4,] 1 2 1
#[5,] 2 1 1
#[6,] 2 2 2
#[7,] 2 1 2
#[8,] 2 2 1