项目未正确添加到r中预先分配的向量中

Question

我试图将数据添加到预先分配的列表中，但它只起到一半的作用。

x <- c(1,2,3,4,5,6,7,8,9,10)
y <- c(0.5,1,1.5,2,2.5,3,3.5,4,4.5,5)
x_num      <- rep(0,length(x))
y_num      <- rep(0,length(y))
for (i in x){
x_diff <- i - mean(x)
print(x_diff)
x_num[i]  <- x_diff
}
[1] -4.5
[1] -3.5
[1] -2.5
[1] -1.5
[1] -0.5
[1] 0.5
[1] 1.5
[1] 2.5
[1] 3.5
[1] 4.5
> x_num
[1] -4.5 -3.5 -2.5 -1.5 -0.5  0.5  1.5  2.5  3.5  4.5
for (i in y){
y_diff <- i - mean(y)
print(y_diff)
y_num[i]  <- y_diff
}
[1] -2.25
[1] -1.75
[1] -1.25
[1] -0.75
[1] -0.25
[1] 0.25
[1] 0.75
[1] 1.25
[1] 1.75
[1] 2.25
> y_num
[1] -1.25 -0.25  0.75  1.75  2.25  0.00  0.00  0.00  0.00  0.00

计算x_diff和y_diff的正确值，但只有x_num被正确填充。我这里缺什么了吗？

Answer 1

您需要元素编号，因此可能需要使用seq_along和子集y[i]

for (i in seq_along(y)){
y_diff <- y[i] - mean(y)
print(y_diff)
y_num[i]  <- y_diff
}
# [1] -2.25
# [1] -1.75
# [1] -1.25
# [1] -0.75
# [1] -0.25
# [1] 0.25
# [1] 0.75
# [1] 1.25
# [1] 1.75
# [1] 2.25

y_num
# [1] -2.25 -1.75 -1.25 -0.75 -0.25  0.25  0.75  1.25  1.75  2.25

然而，R是矢量化的，所以你可以只做

y - mean(y)
# [1] -2.25 -1.75 -1.25 -0.75 -0.25  0.25  0.75  1.25  1.75  2.25