CODEWITHSUNDEEP
rfunctionif-statement
Ash A
Ash A

Reputation: 157

How to check if data table has empty rows?

I am writing function that filters out some random data from a data table random according to an id value ,but I want it first to check if there is actual data rows in the data table first. I ended up writing an if statement and using is.null but its still for the condition but its not working and ends up accessing the else statement and then giving me an error. The code is posted below, please help me 

new.filterID <- function(DataTable,id) {
  if(DataTable == is.null){
    return(print("No Data Available: ",id))
  } else { filtered <- subset(DataTable, ID == id)
    return(aggregate(Value ~ YEAR_WW, filtered, mean))
  }
}
filteredData <- new.filterID(random, 213)

The error I get when I run this is

Error in aggregate.data.frame(mf[1L], mf[-1L], FUN = FUN, ...) : 
  no rows to aggregate

Also below the empty data table random 

Value   YEAR_WW

Upvotes: 1

Views: 18921

Answers (1)

Gustavo
Gustavo

Reputation: 126

I think you can use nrow if you just want to check if the number of lines is zero:

new.filterID <- function(DataTable,id) {
  if(nrow(DataTable) == 0){
   return(print("No Data Available: ",id))
  } else { 
   filtered <- subset(DataTable, ID == id)
   return(aggregate(Value ~ YEAR_WW, filtered, mean))
  }
}
filteredData <- new.filterID(random, 213)

However, if you want to check if data.table is null you can check if there is some column on it:

new.filterID <- function(DataTable,id) {
  if(nrow(DataTable) == 0 & length(names(DataTable)) == 0){
   return(print("No Data Available: ",id))
  } else { 
   filtered <- subset(DataTable, ID == id)
   return(aggregate(Value ~ YEAR_WW, filtered, mean))
  }
}
filteredData <- new.filterID(random, 213)

Data table has not a method to check if it is null, yet.

Upvotes: 6

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