Saving function output to specific place in dataframe - r

Question

I'm working on a function that predicts using a gbm model, one row at a time. Then, I want to save the predicted value in a specific place in my DF so that the next value can be predicted with that output included. Basically, a prediction with a lagged dependent variable. Below is a snippet of my data
DEC AAA_CCC BBBB LLLLL DDD_SHR ST_DSC WKG.P WKG.P.1T _CHNG XXXX_pr XXXX_pr_r XXXX_vol XXXX_.T.1.
38 0 0.99 0 0 0.51 8.28 0 0 6.04 2.84 2.84 10.49 9.83
39 0 0.99 0 0 0.51 8.27 0 0 5.97 2.75 2.75 10.33 10.49
40 0 1.04 0 0 0.51 8.27 0 0 6.01 2.81 2.81 10.58 10.33
41 0 0.98 0 0 0.51 8.28 0 0 5.99 2.87 2.87 9.49 10.58
42 0 0.98 0 1 0.52 8.27 0 0 6.10 2.81 2.81 10.35 9.49
43 0 0.95 0 1 0.51 8.27 0 0 6.01 2.72 2.71 10.67 10.35
XXXX_wd XXXX_ICP_A XXXX_ICP_A_.T.1.
38 4.41 0 1
39 4.33 1 0
40 4.36 0 1
41 4.32 1 0
42 4.19 0 1
43 4.25 1 0
This function needs to: find columns with specific names within a DF, check if there are 0s inside, if yes - predict a value based on the row with a 0 in it. Then, save the predicted value in that 0 place, and in a different column with a 0. Keep repeating that until there are no more 0s in the 'vol' column.
I've come up with this:
PREDICTION<-function (a, model)
{
vol<-select(a, ends_with("vol"))
vol_1<-select(a, ends_with("vol_.T.1."))
while (min(which(a[,colnames(vol)]== 0))!=0) {
PRED<-predict(model, a[min(which(a[,colnames(vol)]== 0)),])
a[[min(which(a[,colnames(vol_1)]== 0)),colnames(vol_1)]]<<-print(PRED)
a[[min(which(a[,colnames(vol)]== 0)),colnames(vol)]]<<-print(PRED)
}}
It prints the right values but doesn't save them the way I wanted. So the while part also doesn't work - values are not saved properly so it loops over the same row forever. I've tried replacing the print with return which didn't change anything. I don't really know where to go from here so I appreciate any help.

Answer 1

I have found a solution - definitely not elegant I will work on improving it. Posting if anyone is interesed.
I simplified the loop withing my function - for instead of while. The rows I'm working on are always in the same range so this helped even visually make the code easier to look at. I will be messing with this more so that might make a comeback to make the code more universal.
PREDICTION <- function(a, model)
{
vol <- select(a, ends_with("vol"))
vol_1 <- select(a, ends_with("vol_.T.1."))
for (i in 54:72) {
a[[i,colnames(vol)]] <- print(predict(model, a[i,]))
a[[i+1,colnames(vol_1)]] <- print(predict(model, a[i,]))
}
return(a)
}
Then I use mapply to map this function over my DF which contains dataframes and models to use.
LISTA$DF <- mapply(PREDICTION, a=LISTA$DF, model = LISTA$GBM)
Essentially this was mostly a syntax problem on my end. Just goes to show how much more I have to learn to be able to code more efficiently and functionally.