Excluding rows with NAs in column-wise calculations - r

Question

I have the below function:
colNames = c(1,4)
myfun = function(a,b){
test$result = 0.0
for (i in colNames)
{
test$result = test$result + (test[,i] * exp(-a*test[,i+1]) * exp(b*test[,i+2]))
}
return(test$result)
}
I am basically trying to multiply 3 columns in a sequence (by performing exp operation on i+1 and i+2th columns and multiplying them with col i) and adding their result to a similar operation done to the next 3 columns.
However, I have several null values and whenever I encounter a row in test[,i] with a null value, I want to exclude it from the calculation and perform the next loop.
I mean rows with null values in test[,i] should not be used in the calculation of test$result. Is there anyway to do this?
Sample data:
2 1708.637715 21.30199589 1 408.4464296 19.8614872
1 1708.637715 21.30199589 1 408.4464296 19.8614872
2 1708.637715 21.30199589 1 408.4464296 19.8614872
1 1708.637715 21.30199589 1 408.4464296 19.8614872
6 1708.637715 21.30199589 NA 408.4464296 19.8614872
0 1708.637715 21.30199589 NA 408.4464296 19.8614872
My first iteration should run normally, but in the next iteration only columns 1 to 4 have to be used in the addition
Please help

Answer 1

You simply have to filter out any rows with NA before you enter the loop. To do that the code would be:
test <- test[!apply(is.na(test), 1, any),]
So then if you alter the function to:
new.myfun = function(a,b){
test <- test[!apply(is.na(test), 1, any),]
test$result = 0.0
for (i in colNames)
{
test$result = test$result + (test[,i] * exp(-a*test[,i+1]) * exp(b*test[,i+2]))
}
return(test$result)
}
new.myfun(1,1)
With the output:
[1] 1.736616e-169 1.736616e-169 1.736616e-169 1.736616e-169
Which is hopefully what you're trying to achieve.
You can explicitly iterate through rows (or use apply function):
new.myfun = function(a,b){
check.for.na <- function(x,y,z, a, b) {
if(any(is.na(x), is.na(y), is.na(z))){
return(0)
}
return(x*exp(-a*y)*exp(-b*z))
}
result = rep(0, length(test))
for (ROW in 1:length(test)){
for (i in colNames)
{
check_here_for_na <- check.for.na(test[ROW,i], test[ROW,i+1], test[ROW,i+2], a, b)
result[ROW] = result[ROW] + check_here_for_na
}
}
return(result)
}
new.myfun(1,1)