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I am using randomForest function from randomForest package to find the most important variable: my dataframe is called urban and my response variable is revenue which is numeric.

urban.random.forest <- randomForest(revenue ~ .,y=urban$revenue, data = urban, ntree=500, keep.forest=FALSE,importance=TRUE,na.action = na.omit)

I get the following error: 

Error in randomForest.default(m, y, ...) : data (x) has 0 rows

on the source code it is related to x variable:

n <- nrow(x) p <- ncol(x) if (n == 0) stop("data (x) has 0 rows")

but I cannot understand what is x.

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    You are mixing the formula and the default methods. If you pass a formula to randomForest you shouldn't pass the y value again, because then the function assumes that the formula is the x value and things go wrong. Commented Mar 24, 2014 at 12:14
  • I removed y=urban$revenue but the error still exists: Error in randomForest.default(m, y, ...) : data (x) has 0 rows Commented Mar 24, 2014 at 12:19
  • I have a new error also: In addition: Warning message: In randomForest.default(m, y, ...) : The response has five or fewer unique values. Are you sure you want to do regression? Although my response variable has 58 unique values length(unique(urban$revenue))# ==58 Commented Mar 24, 2014 at 12:21
  • The error is probably in your data, because your line works fine with iris data urban.random.forest <- randomForest(Species ~ ., data=iris, ntree=500, keep.forest = FALSE,importance = TRUE, na.action = na.omit) Commented Mar 24, 2014 at 12:22

2 Answers 2

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I solved that. I had some columns that all their values were NA or the same. I dropped them and it went OK. my columns classes were character, numeric and factor.

 candidatesnodata.index <- c() for (j in (1 : ncol(dataframe))) { if ( is.numeric(dataframe[ ,j]) & length(unique(as.numeric(dataframe[ ,j]))) == 1 ) {candidatesnodata.index <- append(candidatesnodata.index,j)} } dataframe <- dataframe[ , - candidatesnodata.index]
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3

I have had a similar problem and it stemmed from the fact that I was passing in a string version of the call

y ~ x1 + .... xn

to the formula argument of the randomForest call. The simple fix was to cast the input to as.Formula().

I hope this saves anyone some time!

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