R: Passing the index of the corresponding data frame (from a list of data frames) in a function within lapply

Question

I have a list of 9 data frames list_dataframes read from files and a function func_modification to modify them. I would like to pass the value of pos the index of the corresponding data frame in list, so that individual rows can have their respective dmv and method names. How to do that?

dmv <- c(rep("MC", 3), rep("MSM", 3), rep("Random", 3))
method <- rep(c("COM-0.5", "IDT", "LB"), 3)

func_modification <- function(d, pos) {  
  d[,1] <- d[,1]/3600   
  d[,3] <- NA
  d[,3] <- dmv[pos]
  d[,4] <- method[pos]
} 

list_df <- list()
list_df <- lapply(list_dataframes, func_modification, pos=3) // Works
list_df <- lapply(list_dataframes, func_modification, pos=1:9) // Showing error

Answer 1

You can try Map to change the corresponding dataframes with each element of 'pos'

Map(func_modification, list_dataframes, pos= 1:3)

Or using lapply

lapply(seq_along(list_dataframes), function(i) 
            func_modification(list_dataframes[[i]], pos=i))

where func_modification is

func_modification <- function(d, pos) {  
   d[,1] <- d[,1]/3600   
   d[,3] <- NA #not sure if this needed
   d[,3] <- dmv[pos]
   d[,4] <- method[pos]
   d #return the data 
 } 

data

set.seed(24)
list_dataframes <- lapply(1:3, function(i) 
  as.data.frame(matrix(sample(1:10, 5*20, replace=TRUE), ncol=5)))