# Defining Variables from a Matrix for 10-Fold Cross Validation

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## Defining Variables from a Matrix for 10-Fold Cross Validation

 Good afternoon, I am trying to run a 10-fold CV, using a matrix as my data set. Essentially, I want "y" to be the first column of the matrix, and my "x" to be all remaining columns (2-257). I've posted some of the code I used below, and the data set (called "zip.train") is in the "ElemStatLearn" package. The error message is highlighted in red, and the corresponding section of code is bolded. (I am not concerned with the warning message, just the error message). The issue I am experiencing is the error message below the code: I haven't come across that specific message before, and am not exactly sure how to interpret its meaning. What exactly is this error message trying to tell me?  Any suggestions or insights are appreciated! Thank you all, Matthew Campbell > library (ElemStatLearn) > library(kknn) > data(zip.train) > train=zip.train[which(zip.train[,1] %in% c(2,3)),] > test=zip.test[which(zip.test[,1] %in% c(2,3)),] > nfold = 10 > infold = sample(rep(1:10, length.out = (x))) Warning message: In rep(1:10, length.out = (x)) :   first element used of 'length.out' argument > *> mydata = data.frame(x = train[ , c(2,257)] , y = train[ , 1])* > > K = 20 > errorMatrix = matrix(NA, K, 10) > > for (l in nfold) + { +   for (k in 1:20) +   { +     knn.fit = kknn(y ~ x, train = mydata[infold != l, ], test = mydata[infold == l, ], k = k) +     errorMatrix[k, l] = mean((knn.fit\$fitted.values - mydata\$y[infold == l])^2) +   } + } Error in model.frame.default(formula, data = train) :   variable lengths differ (found for 'x')         [[alternative HTML version deleted]] ______________________________________________ [hidden email] mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code.