How do I write an infix function?

I am trying to write an infix function called %#% that will operate on two vectors x and y. The operation x%#%y should return a vector that is the same length as x and y. Element i of the returned vector should be x[i]+y[i] if x[i]>0 and y[i]>0, 0 if x[i]>0 and y[i]<0 or if x[i]<0 and y[i]>0, and -x[i]-y[i] if x[i]<0 and y[i]<0. An error should be returned if the vectors have different lengths.

x <- rnorm(10)
y <- rnorm(10)
'%#%' <- function(x,y) { 
for (i in 1:10)
{
if (x[i]>0 & y[i]>0) paste(x[i]+y[i])
if (x[i]>0 & y[i]<0) paste(0)
if (x[i]<0 & y[i]>0) paste(0)
if (x[i]<0 & y[i]<0) paste(-x[i]-y[i]) 
else stop("Vectors have different lengths")
}}
x%#%y

It just keeps giving me the error message.

I recommend to:

• not use # because this symbol is reserved for comments in R
• use a vectorized approach
• think about what should happen if x or y are zero

You could try something along the lines:

`%ooo%` <- function(x,y) { 
    if(length(x)!=length(y))
        stop("Vectors have different lengths")
    tmp <- ifelse(x>0 & y>0, x+y, -x-y)
    tmp[(x>0 & y<0) | (x<0 & y>0)] <- 0
    tmp
}

x <- rnorm(10)
y <- rnorm(10)

rep(1, 5) %ooo% rep(1, 6)
## Error in rep(1, 5) %ooo% rep(1, 6) : Vectors have different lengths

rep(1, 5) %ooo% -2:2
## [1]  0  0 -1  2  3