[FIXED] What is the correct syntax when calling a variable name from within a function

Issue

I have data as follows:

library(data.table)
set.seed(1) 
year = c(rep(2000,5), rep(2001,5),  rep(2002,5),  rep(2003,5),  rep(2004,5))
DT <- data.table(panelID = sample(10,10),                                                   
                      some_type = as.factor(sample(0:5, 6)),                                             
                      some_other_type = as.factor(sample(0:5, 6)),         
                      Group = c(rep(1,20),rep(2,20),rep(3,20),rep(4,20),rep(5,20)),
                      wt = 15*round(runif(100)/10,2),
                      Income = round(rnorm(10,-5,5),2),
                      Income_proxy = round(rnorm(10,-6,6),2),
                      year = rep(year,4),
                      Happiness = sample(10,10),
                      Sex = round(rnorm(10,0.75,0.3),2),
                      Age = sample(100,100),
                      Height= 150*round(rnorm(10,0.75,0.3),2))   

I am trying to write a function that automatically creates certain calculations, just by providing the grouping variables.

calulate_relative_dev <- function(DT, varA="Income", varB="Income_proxy", groups, years=NULL) {
  if (is.null(years)) {
    out_names <- paste0("rel_deviation_", groups[i]) 
    for (i in seq_along(groups)) {
      setDT(DT)[, (out_names[i]) := 100*mean((varA - varB) / varA), by=eval(groups[i])]
    }
  } else if (!is.null(years))
    out_names <- paste0("rel_deviation_", groups[i], years[i]) 
    for (i in seq_along(groups)) {
      for (j in seq_along(years)) {
        setDT(DT)[, (out_names[i]) := 100*mean((varA - varB) / varA), by=eval(groups[i], years[i])]
      }
    }
}

In order to do:

calulate_relative_dev(DT, groups = c("Group","some_type"))

and

calulate_relative_dev(DT, groups = c("Group","some_type"), years=year))

But when I do, I get the following error:

Error in h(simpleError(msg, call)) : 
  error in evaluating the argument 'x' in selecting a method for function 'mean': object 'Income' not found
Called from: h(simpleError(msg, call))

If I try to put Income in quotes, I get:

Error in h(simpleError(msg, call)) : 
  error in evaluating the argument 'x' in selecting a method for function 'mean': non-numeric argument to binary operator
Called from: h(simpleError(msg, call))

How should I write the syntax here?

Solution

Based on your comment/reply to my question, I understand years is intended to be a logical. Here is one possible function:

calulate_relative_dev <- function(DT, varA="Income", varB="Income_proxy", groups, year=FALSE) {
  dt <- copy(DT)
  setnames(dt, old = c(varA, varB), new = c("varA", "varB"))
  for (i in seq_along(groups)) {
    out_names <- paste0("rel_deviation_", groups)
    if(year) out_names <- paste0(out_names, "_by_year")
    dt[, c(out_names[i]) := 100*mean((varA - varB) / varA), by=c(groups[i], if(year){"year"})]
  }
  setnames(dt, old = c("varA", "varB"), new = c(varA, varB))
  return(dt[])
}

calulate_relative_dev(DT, groups = c("Group","some_type"))
calulate_relative_dev(DT, groups = c("Group","some_type"), year=TRUE)

I did temporary renames to make the data.table code simpler to read/write. Returning dt[] ensures the data.table is printed after the function is evaluated.

Answered By - Hutch3232

Answer Checked By - Katrina (PHPFixing Volunteer)