Function works normally. But when used with sapply in order to pass each value of a vector as one of-CodePudding

Sorry for the bad phrasing of the question!

I created a function, abc, and it works fine with my data table, DT, by itself.

#function
abc <- function(DT, ucol="u", vcol="v", xdiff = 3) {
  #find n
  result1 = DT[DT[,x2:= x_coord.   xdiff ], on=.(y_coord, x_coord=x2), nomatch=0]
  result1[, ucol_values:=get(ucol)]
  n_points <- nrow(result1)                   #N
  
  #find (ui-uj)*(vi-vj)
  result2 = result1
  result[, prod:=(get(ucol)-get(paste0("i.",ucol)))*(get(vcol)-get(paste0("i.",vcol)))][, .(row_a=row, row_b=i.row, prod)]
  sum_prod_result<- sum(result2$prod)
    
  resultlist<- list("xdiff"=xdiff, "sum of products"=sum_prod_result, "n"=n_points)
  
  return(resultlist)
}

>abc(DT)
$`xdiff`
[1] 5

$`sum of products`
[1] -0.731064

$n
[1] 43

I have a vector x and I want to repeat the function with xdiff equal to each value of x.

x <- (5,10,15,20,25)

sapply<- (xdiffs, abc, xdiff=x)

But I get the following error with sapply:

Error in :=(x2, x_coord. xdiff) : Check that is.data.table(DT) == TRUE. Otherwise, := and :=(...) are defined for use in j, once only and in particular ways. See help(":=").

I checked the class of DT and it is a data table. I'm not sure how to fix this issue.

CodePudding user response：

sapply iterates only over the first argument provided, so you would need to change the function call to something like:

sapply(x, function(i) abc(DT, xdiff = i))