Why is R printing 3 rows and 1 columns as the answer

Question

x <- data.frame(Level=c(6.5))
x_poly <- poly(x$Level, 4, raw=TRUE)
x1 <- cbind(x, x_poly[, 2:4])

This is my code and whenever I was using cbind for some reason it was printing 3 rows and column even though both x and x_poly have only 1 row.

x_poly <- as.data.frame(x_poly[, 2:4])
print(dim(x_poly))

I tried to print the dimensions of x_poly and x_poly[,2:4]. For some reason x_poly shows 1 row on;y but x_poly[2:4] shows 3 rows.

Answer 1

When extracting using `[`, R uses drop (see ?drop), to coerce to the lowest possible dimensions.

So from the matrix,

> dim(x_poly)
[1] 1 4

you will get a vector.

> dim(x_poly[, 2:4])
NULL

We can do drop=FALSE.

> dim(x_poly[, 2:4, drop=FALSE])
[1] 1 3

Thus, what you're looking for is

> cbind(x, x_poly[, 2:4, drop=FALSE])
  Level     2       3        4
1   6.5 42.25 274.625 1785.062

---

Data:

x <- data.frame(Level=c(6.5))
x_poly <- poly(x$Level, 4, raw=TRUE)