In general this error message means that you have tried to use indexing on a function. You can reproduce this error message with, for example
mean[1]
## Error in mean[1] : object of type 'closure' is not subsettable
mean[[1]]
## Error in mean[[1]] : object of type 'closure' is not subsettable
mean$a
## Error in mean$a : object of type 'closure' is not subsettable
The closure mentioned in the error message is (loosely) the function and the environment that stores the variables when the function is called.
In this specific case, as Joshua mentioned, you are trying to access the url function as a variable. If you define a variable named url, then the error goes away.
As a matter of good practise, you should usually avoid naming variables after base-R functions. (Calling variables data is a common source of this error.)
There are several related errors for trying to subset operators or keywords.
`+`[1]
## Error in `+`[1] : object of type 'builtin' is not subsettable
`if`[1]
## Error in `if`[1] : object of type 'special' is not subsettable
If you're running into this problem in shiny, the most likely cause is that you're trying to work with a reactive expression without calling it as a function using parentheses.
library(shiny)
reactive_df <- reactive({
data.frame(col1 = c(1,2,3),
col2 = c(4,5,6))
})
While we often work with reactive expressions in shiny as if they were data frames, they are actually functions that return data frames (or other objects).
isolate({
print(reactive_df())
print(reactive_df()$col1)
})
col1 col2
1 1 4
2 2 5
3 3 6
[1] 1 2 3
But if we try to subset it without parentheses, then we're actually trying to index a function, and we get an error:
isolate(
reactive_df$col1
)
Error in reactive_df$col1 : object of type 'closure' is not subsettable