Change length of an object using the get() function R-CodePudding

I'm writing a function to analyse .csv files in a directory on my hard drive, using a series of for and while loops (I know for loops are unpopular in R, but they're good for what I need).

The function creates a number of data-frames, and performs actions on each one in turn before overwriting them and moving on to the next file in the directory to repeat the action.

The part of the code that does not work so far is the creation of a matrix from vectors taken from the data files being analysed. A simplified version of the code is shown below:

data1 <- seq(1, 10, 1)
data2 <- seq(1, 7, 1)
data3 <- seq(1, 5, 1)

n <- max(length(data1), length(data2), length(data3))

k <- c(1, 2, 3)

for(a in k){
  
  if(a == 1){
    
    length(get(paste("data", a, sep = ""))) <- n
    data_matrix <- get(paste("data", a, sep = ""))
    
  }else{
    
    while(exists(paste("data", a, sep = ""))){
      
      length(get(paste("data", a, sep = ""))) <- n
      data_matrix <- cbind(data_matrix, get(paste("data", a, sep = "")))
      
    }
    
  }
  
}

The nature of my data is that the length of the columns in my datasets vary with each data collection, so I've adapted a technique found in this post that deals with using cbind to bind objects of a different length without replication of the data within the smaller objects.

The issue I have when trying to implement this code is I get the error message:

Error in length(get(paste("data", a, sep = ""))) <- n : target of assignment expands to non-language object

I'm guessing the issue is that the function get() cannot be used to select items in the Global Environment and to modify them in this way.

CodePudding user response：

You could use:

get("x")[1:n]

to get a vector called "x" padded with NA to length n.

That is:

> x=1:3
> n=10
> get("x")[1:n]
 [1]  1  2  3 NA NA NA NA NA NA NA

Having said that, this is a neater way to get the matrix you want (hopefully you can adapt to your scenario):

> datalist <- list(data1, data2, data3)
> maxlength <- max(lengths(datalist))
> sapply(datalist, function(x) x[1:maxlength]  )
      [,1] [,2] [,3]
 [1,]    1    1    1
 [2,]    2    2    2
 [3,]    3    3    3
 [4,]    4    4    4
 [5,]    5    5    5
 [6,]    6    6   NA
 [7,]    7    7   NA
 [8,]    8   NA   NA
 [9,]    9   NA   NA
[10,]   10   NA   NA