vector to dataframe in r given length of vector - r

Question

I have vectors of different lengths. For instance:
df1
[1] 1 95 5 2 135 4 3 135 4 4 135 4 5 135 4 6 135 4
df2
[1] 1 70 3 2 110 4 3 112 4
I'm trying to write a script in R in order to have any vector enter the function or for loop and it returns a dataframe of three columns. So a separate dataframe for each input vector. Each vector is a multiple of three (hence, the three columns). I'm fairly new to R in terms of writing functions and can't seem to figure this out. Here was my attempt:
newdf = c()
ld <- length(df1)
ld_mult <- length(df1)/3
ld_seq <- seq(from=1,to=ld,by=3)
ld_seq2 < ld_seq +2
for (i in 1:ld_mult) {
newdf[i,] <- df1[ld_seq[i]:ld_seq2[i]]
}
the output I want for df1 would be:
1 95 5
2 135 4
3 135 4
4 135 4
5 135 4
6 135 4

Answer 1

Here's an example of how you could use matrix for that purpose:
x <- c(1, 95, 5,2, 135, 4, 3, 135, 4)
as.data.frame(matrix(x, ncol = 3, byrow = TRUE))
# V1 V2 V3
#1 1 95 5
#2 2 135 4
#3 3 135 4
And
y <- c(1, 70, 3, 2, 110, 4, 3, 112, 4)
as.data.frame(matrix(y, ncol = 3, byrow = TRUE))
# V1 V2 V3
#1 1 70 3
#2 2 110 4
#3 3 112 4
Or if you want to make it a custom function:
newdf <- function(vec) {
as.data.frame(matrix(vec, ncol = 3, byrow = TRUE))
}
newdf(y)
#V1 V2 V3
#1 1 70 3
#2 2 110 4
#3 3 112 4
You could also let the user specify the number of columns he wants to create with the function if you add another argument to newdf:
newdf <- function(vec, cols = 3) {
as.data.frame(matrix(vec, ncol = cols, byrow = T))
}
Now, the default number of columns is 3, if the user doesnt specify a number. If he wants to, he could use it like this:
newdf(z, 5) # to create 5 columns
Another nice little addon for the function would be a check if the input vector length is a multiple of the number of columns specified in the function call:
newdf <- function(vec, cols = 3) {
if(length(vec) %% cols != 0) {
stop("Number of columns is not a multiple of input vector length. Please double check.")
}
as.data.frame(matrix(vec, ncol = cols, byrow = T))
}
newdf(x, 4)
#Error in newdf(x, 4) :
# Number of columns is not a multiple of input vector length. Please double check.
If you had multiple vectors sitting in a list, here's how you could convert each of them to be a data.frame:
> l <- list(x,y)
> l
#[[1]]
#[1] 1 95 5 2 135 4 3 135 4
#
#[[2]]
#[1] 1 70 3 2 110 4 3 112 4
> lapply(l, newdf)
#[[1]]
# V1 V2 V3
#1 1 70 3
#2 2 110 4
#3 3 112 4
#
#[[2]]
# V1 V2 V3
#1 1 70 3
#2 2 110 4
#3 3 112 4