What is the best way to create dynamic array and assign values to it in a for loop using R

Question

I want to get values from an excel file, and assign certain values of them to arrays. At the beginning I tried the code below, and it worked. But after restarting r studio, and did everything again, it shows me this error

Error in USComp2005_2000_3000[m] = USComp2005$SIC[i] : object 'USComp2005_2000_3000' not found

I don't know how it worked in the beginning!

library(readxl)
USComp2005 <- read_excel("USCompanies2005.xlsx",sheet = "Data")
getValues <- function() 
{
 n=0
 m=0
 for (i in 1:6992) {
    if ((USComp2005$SIC[i] >= 6000) && (USComp2005$SIC[i] < 7000)) {
         n=n+1
         USComp2005_6000[n] = USComp2005$SIC[i]
     }
     else if ((USComp2005$SIC[i] >= 2000) && (USComp2005$SIC[i] < 4000)) {
         m=m+1
         USComp2005_2000_3000[m] = USComp2005$SIC[i]
     }
 }
}

hm `USComp2005_6000 <- USComp2005$SIC[(USComp2005$SIC >= 6000) & (USComp2005$SIC < 7000)]`? — jogo, Apr 19 '17 at 09:31
Didn't work. When I run the function, the variable USComp2005_6000 isn't created. — Ali Zuhair, Apr 19 '17 at 09:59
It works: `set.seed(42); d <- data.frame(a=rnorm(100), b=rnorm(100), c=sample(1100:2000, 100)); d[(d$a>0.7) & (d$b< -0.8),]; d$c[(d$a>0.7) & (d$b< -0.8)]` Please give a reproducable example! [mcve] and http://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example — jogo, Apr 19 '17 at 11:44

score 0 · Answer 1 · answered Apr 19 '17 at 12:23

Variables created inside a for loop or a function in R have local scope (i.e. they are reachable only from within that loop). You should initialize the vectors before the loop, and then fill them. Something like:

USComp2005_6000 = USComp2005_2000_3000 = NULL
for (condition) {
  ...
  USComp2005_6000[n] = ...
  ...
}

One can also use global assignment:

function(){ USComp = ... } # USComp is local

USComp = NULL; function(){ USComp = ... } # global by initialization

function(){ USComp <<- ... } # global by assignment

But for your task, @jogo's vectorized solution in the comment is the best. Again, just make sure to initialize the vectors, or use global scope.

What is the best way to create dynamic array and assign values to it in a for loop using R

1 Answers1