Calling a character string into object names within a function

Question

I've currently got a very lengthy and repetitive bit of code for data normalisation and inversion ((x-min)/(max-min)*-1)+1) that I want to clean up a bit.

This is a small sample of what it currently looks like:

W3_E1_Norm_New <- W3_E1_Average%>%
  mutate(W3_E1_Norm_New = ((W3_E1_zoo-W3_E1_Min)/(W3_E1_Max-W3_E1_Min)*-1)+1)
W3_E2_Norm_New <- W3_E2_Average%>%
  mutate(W3_E2_Norm_New = ((W3_E2_zoo-W3_E2_Min)/(W3_E2_Max-W3_E2_Min)*-1)+1)
W3_E3_Norm_New <- W3_E3_Average%>%
  mutate(W3_E3_Norm_New = ((W3_E3_zoo-W3_E3_Min)/(W3_E3_Max-W3_E3_Min)*-1)+1)

Each 'W3_E1' refers to a sample ID, and at present each sample ID requires the two lines of code to be written out each time. Ideally I'd like to write a function which can call a character string (Sample_IDs) into the names of each data frame, so something like

a_Norm_New

would return

W3_E1_Norm_New

then

W3_E2_Norm_New

etc.

Is there a way to write a function that could accomplish this?

Many thanks

Answer 1

I don't have your data but this should work. Define a function:

my_fun <- function (x) {

  norm_new <- paste0(x,"_Norm_New")
  average <- paste0(x,"_Average")
  zoo <- paste0(x, "_zoo")
  min <- paste0(x, "_Min")
  max <- paste0(x, "_Max")

   df <- get(average) %>%
    mutate(new_norm = ((zoo - min) / (max - min) * - 1) + 1)

  assign(df, norm_new)
}

Then run a for loop:

Sample_IDs <- c("W3_E1", "W3_E2", "W3_E3")

for (i in Sample_IDs) {
  my_fun(i)
}

Answer 2

With data.table , it is very easy to write functions that use quoted variable names (see a blog post I wrote on the subject ).

Here, we paste the pattern of your column name everywhere with the sufx variable:

library(data.table)

normalize <- function(dt, sufx = "W3_E1"){
  df <- as.data.table(dt)
  df[, (paste0(sufx,"_Norm_New")) := (
    (get(paste0(sufx,_zoo)) - get(paste0(sufx,"_Min"))
     )/(
       get(paste0(sufx,"_Max")) - get(paste0(sufx,"_Min"))
        )*-1)+1)
}

Here the code is not easy to read because I wanted to show that this can be done in one line but you can give more readability easily.

In this solution, you use get to unquote your variable name.