Application of the assign function in loops

This happens because assign modifies the parent environment. In the case of for, the parent environment is the global environment itself. So the variables appear to you.

In the case of a function being called by map or lapply , the parent environment is the environment of the calling function itself, and that environment is destroyed shortly after the function is executed.

You can see the environment that the function is using with the environment function:

> for(i in 1:6){
+   names<-str_c('var',i)
+   print(environment())
+   assign(names,runif(30,20,100))
+ }
<environment: R_GlobalEnv>
<environment: R_GlobalEnv>
<environment: R_GlobalEnv>
<environment: R_GlobalEnv>
<environment: R_GlobalEnv>
<environment: R_GlobalEnv>


> lapply(1:6,function(i){
+   names<-str_c('var',i)
+   print(environment())
+   assign(names,runif(30,20,100))
+ })
<environment: 0x14eec3a0>
<environment: 0x2bd9e368>
<environment: 0x13b43ae0>
<environment: 0xe7213c0>
<environment: 0x13dc00d8>
<environment: 0x1a7aab10>

One way to modify lapply or map to work the way you imagine it is to specify the environment for the assign function:

lapply(1:6,function(i){
  names<-str_c('var_lapply_',i)
  assign(names,runif(30,20,100), envir = .GlobalEnv)
})

Note: If you need to use assign you are probably making a code that would look better if you used a named list.

Worth reading the chapter on Advanced R environments: link

assign creates new variables in environment of anonymous function, not .GlobalEnv . For this we use the envir argument.

library(tidyverse)

set.seed(1234)
for(i in 1:6){
  names<-str_c('x',i)
  assign(names,runif(30, 20, 100))
}


set.seed(1234)
lapply(1:6, function(i){
  names <- str_c('y', i)
  assign(names, runif(30, 20, 100), envir = .GlobalEnv)
})

identical(x1, y1)
#[1] TRUE

set.seed(1234)
map(1:6, function(i){
  names <- str_c('z', i)
  assign(names, runif(30, 20, 100), envir = .GlobalEnv)
})

identical(x1, z1)
#[1] TRUE