{"action":"opened","issue":{"url":"https://api.github.com/repos/mlr-org/mlr/issues/893","repository_url":"https://api.github.com/repos/mlr-org/mlr","labels_url":"https://api.github.com/repos/mlr-org/mlr/issues/893/labels{/name}","comments_url":"https://api.github.com/repos/mlr-org/mlr/issues/893/comments","events_url":"https://api.github.com/repos/mlr-org/mlr/issues/893/events","html_url":"https://github.com/mlr-org/mlr/issues/893","id":154905899,"number":893,"title":"Problem with impute learner","user":{"login":"studerus","id":373643,"avatar_url":"https://avatars.githubusercontent.com/u/373643?v=3","gravatar_id":"","url":"https://api.github.com/users/studerus","html_url":"https://github.com/studerus","followers_url":"https://api.github.com/users/studerus/followers","following_url":"https://api.github.com/users/studerus/following{/other_user}","gists_url":"https://api.github.com/users/studerus/gists{/gist_id}","starred_url":"https://api.github.com/users/studerus/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/studerus/subscriptions","organizations_url":"https://api.github.com/users/studerus/orgs","repos_url":"https://api.github.com/users/studerus/repos","events_url":"https://api.github.com/users/studerus/events{/privacy}","received_events_url":"https://api.github.com/users/studerus/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"milestone":null,"comments":0,"created_at":"2016-05-15T12:19:37Z","updated_at":"2016-05-15T12:19:37Z","closed_at":null,"body":"I experienced a problem using imputeLearner for cross-validation. Here's an example:\r\n\r\n    dat = data.frame(y = rnorm(10), a = c(NA, rnorm(9)), b = rnorm(10))\r\n    task = makeRegrTask(data = dat, target = \"y\")\r\n    impLrn = imputeLearner(makeLearner(\"regr.rpart\"))\r\n    lrn = makeImputeWrapper(makeLearner(\"regr.lm\"), cols = list(a = impLrn))\r\n\r\n    #works\r\n    train(lrn, tsk)\r\n\r\n    #does not work\r\n    holdout(lrn, task)\r\n\r\n> [Resample] holdout iter: 1\r\n> Error in holdout(lrn, task) : \r\n>   Assertion on 'newdata' failed: Must have at least 1 rows, but has 0 rows.\r\n\r\nDoes anybody know, what's the problem here? Someone else has also mentioned this problem on [stackoverflow](http://stackoverflow.com/questions/36811709/mlr-package-error-for-imputation)\r\n  "}}