[R] When using require(), why do I get the error message "Error in if (!loaded) { : the condition has length > 1" ?

[Kelly Thompson]

# Below, when using require(), why do I get the error message "Error
in if (!loaded) { : the condition has length > 1" ?

# This is my reproducible code:

#create a vector with the names of the packages I want to use
packages_i_want_to_use <- c('base', 'this_pac_does_not_exist')

# Here I get error messages:
require( packages_i_want_to_use[1] )
#Error in if (!loaded) { : the condition has length > 1

require( packages_i_want_to_use[2] )
#Error in if (!loaded) { : the condition has length > 1

# Here I get what I expect:
require('base')

require('this_pac_does_not_exist')
#Loading required package: this_pac_does_not_exist
#Warning message:
#In library(package, lib.loc = lib.loc, character.only = TRUE,
logical.return = TRUE,  :
#  there is no package called ‘this_pac_does_not_exist’