xgb.DMatrix Error: The length of labels must equal to the number of rows in the input data

Question

I am using xgboost in R.

I created the xgb matrix fine using a matrix as input, but when I reduce the number in columns in the matrix data, I receive an error.

This works:

> dim(ctt1)

[1] 6401 5901

> xgbmat1 <- xgb.DMatrix(
     Matrix(data.matrix(ctt1)),
     label = as.matrix(as.numeric(data$V2)) - 1
  )

This does not:

> dim(ctt1[,nr])

[1] 6401 1048

xgbmat1 <- xgb.DMatrix(
    Matrix(data.matrix(ctt1[,nr])),
    label = as.matrix(as.numeric(data$V2)) - 1)

Error in xgb.setinfo(dmat, names(p), p[[1]]) : The length of labels must equal to the number of rows in the input data

Answer 1

In my case I fixed this error by changing assign operation:

labels <- df_train$target_feature

Answer 2

It turns out that by removing some columns, there are some rows with all 0s, and could not contribute to model.