R help - Oct 2018 - 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')

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> On Oct 9, 2018, at 3:04 PM, matthew campbell <mcc3qb at virginia.edu>
wrote:
> 
> 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)))
I don't see a definition for x.
> Warning message:
> In rep(1:10, length.out = (x)) :
>  first element used of 'length.out' argument
But apparently it las a length greater than 1 and your are getting a sample
whose length is specified by the first element of x.

>> 
> *> 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')
So the warning above is probably a great clue to the source of this error.

Morale of the tale: Always read the warnings, even if your code proceeds.
> 
> 	[[alternative HTML version deleted]]
> 
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