Error in { : task 1 failed - "could not find function "knn""

Question

I am trying to run a parallel kNN program on R but I get this error:

Error in { : task 1 failed - "could not find function "knn""

This is the program:

library(class)
library(doSNOW)
library(foreach)

train <- read.csv('train.csv')
test <- read.csv('test.csv')
trainY <- read.csv('trainY.csv')
cl <- as.vector(as.matrix(trainY))

system.time(summary(knn(train, test, cl, k=25, prob = TRUE)))


clus <- makeCluster(4)
registerDoSNOW(clus)
countrows=nrow(test)

system.time(foreach( icount(countrows) ) %dopar% {
  summary(knn(train, test, cl, k=25, prob = TRUE))
})

stopCluster(clus)

Solution

You need to call library(class) on each of the nodes. foreach makes this easy via the .packages argument.

system.time(foreach( icount(countrows), .packages="class" ) %dopar% {
  summary(knn(train, test, cl, k=25, prob = TRUE))
})

You might also need to export train, test, and cl.

system.time(
  foreach( icount(countrows), .packages="class",
           .export=c("train","test","cl") ) %dopar% {
    summary(knn(train, test, cl, k=25, prob = TRUE))
  }
)