Change data.table column values dynamically inside a function?-CodePudding

How do you change the values in a data.table column within a function?

DF = data.table(ID = c("b","b","b","a","a","c"), a = 1:6, b = 7:12, c = 13:18)

change_it <- function(data_table) {
    data_table[[column]] <- 73
}

column = 'a'

change_it(DF, column) # Nothing happens because data_table is not a reference (or something)

DF[[column]] <- 73 # The change happens

CodePudding user response：

It works with the := operator like so:

DF = data.table(ID = c("b","b","b","a","a","c"), a = 1:6, b = 7:12, c = 13:18)

change_it <- function(data_table) {
    data_table[, c('a') := 73]
}

change_it(DF) # The change occured

This would change the values in-place.

CodePudding user response：

One way to solve your problem:

change_it <- function(data_table) {
  set(data_table, j="a", value=73)
}

# apply the change
change_it(DF)