[R] Saving misclassified records into dataframe within a loop

From: John Dennison <dennison.john_at_gmail.com>
Date: Thu, 12 May 2011 12:33:21 -0400


Greetings R world,

I know some version of the this question has been asked before, but i need to save the output of a loop into a data frame to eventually be written to a postgres data base with dbWriteTable. Some background. I have developed classifications models to help identify problem accounts. The logic is this, if the model classifies the record as including variable X and it turns out that record does not have X then it should be reviewed(ie i need the row number/ID saved to a database). Generally i want to look at the misclassified records. This is a little hack i know, anyone got a better idea please let me know. Here is an example

library(rpart)

# grow tree

fit <- rpart(Kyphosis ~ Age + Number + Start,

   method="class", data=kyphosis)
#predict

prediction<-predict(fit, kyphosis)

#misclassification index function

predict.function <- function(x){
for (i in 1:length(kyphosis$Kyphosis)) {
#the idea is that if the record is "absent" but the prediction is otherwise
then show me that record
 if (((kyphosis$Kyphosis[i]=="absent")==(prediction[i,1]==1)) == 0 ){    #THIS WORKS
print( row.names(kyphosis[c(i),]))
}
} }

predict.function(x)

Now my issue is that i want to save these id to a data.frame so i can later save them to a database. This this an incorrect approach. Can I save each id to the postgres instance as it is found. i have a ignorant fear of lapply, but it seems it may hold the key.

Ive tried

predict.function <- function(x){
results<-as.data.frame(1)
for (i in 1:length(kyphosis$Kyphosis)) {
#the idea is that if the record is "absent" but the prediction is otherwise
then show me that record
 if (((kyphosis$Kyphosis[i]=="absent")==(prediction[i,1]==1)) == 0 ){    #THIS WORKS

results[i,]<- as.data.frame(row.names(kyphosis[c(i),])) }
} }

this does not work. results object does not get saved. Any Help would be greatly appreciated.

Thanks

John Dennison

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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Thu 12 May 2011 - 16:36:09 GMT

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