"Error in table(pred = prediction, true = W[, 8]) : all arguments must have the same length"

Question

this is my data:

 Anon_Student_Id           Problem_Hierarchy Problem_Name Problem_View Number_Of_Steps Sum_Of_Steps_Duration Sum_Of_Hints result
1      80nlN05JQ6 Unit ES_01, Section ES_01-6         EG21            8               3                    28            0      1
2      80nlN05JQ6 Unit ES_01, Section ES_01-6         EG21            9               3                    37            0      0
3      80nlN05JQ6 Unit ES_01, Section ES_01-6         EG21           10               3                    50            0      0
4      80nlN05JQ6 Unit ES_01, Section ES_01-6         EG22            1               3                    78            0      0
5      80nlN05JQ6 Unit ES_01, Section ES_01-6         EG22            2               3                    41            0      1
6      80nlN05JQ6 Unit ES_01, Section ES_01-6         EG22            3               3                    92            0      0

I'm trying to predict the attribute "result" by SVM model :

model<-svm(result~., scale=FALSE, data=W)

prediction <- predict(model, W[,-8])

table(pred = prediction, true = W[,8])

But I get this error:

"Error in table(pred = prediction, true = W[, 8]) : 
  all arguments must have the same length"

When I checked it I got: length(pred)=2042 and length(true)=2043

Why I'm getting this error?? (I mean- why i'm getting different lengths? "pred" and "true" are supposed to have the same length)

Thanks!

Answer 1

Problem solved: i got rid of all the na values of my data using na.omit(W) and then it worked. thank you!