Error in -title : invalid argument to unary operator Execution halted - r

Question

I used CronJobs to schedule my R markdown to run everyday at 6pm. However, it did not run the script and gave me the following error:Error in -title : invalid argument to unary operator
Execution halted.
The work directory is set to my source location.
Any advice? Thanks!
Here is my code:
---
title: "EXAMPLECODE"
author: "XXXX"
date: "5/4/2020"
output: pdf_document
---
#STEP 1: INSTALL AND LOAD RCURL PACKAGE
```{r}
install.packages("RCurl")
library(RCurl)
```
#STEP 2: READ IN CSV FILE FOR EXAMPLE
```{r}
Example<- getURL("https://www.EXAMPLEURLHERE.csv")
ExampleData <- read.csv(text = Example)
ExampleData
```
#STEP 3: SAVE DATA INTO CSV FILE
```{r}
write.table(ExampleData, file="ExampleData_Update.csv", sep=",")
```

Answer 1

This error is common when you have a unary operator (e.g., -, +, or !) that is out of place. This indicates you have a typo or an object that is empty or not what you think. A guess (since you haven't responded to #AllanCameron's understated suggestion) is that you have a variable named title somewhere, assume that it is numeric or something you can index a vector/list/frame off of, and it is either non-numeric or empty. I can reproduce this precise error with
title <- c()
mtcars[-title,]
# Error in -title : invalid argument to unary operator
title <- "1"
mtcars[-title,]
# Error in -title : invalid argument to unary operator
If you want a stack-trace on errors, then you might take a suggestion from https://renkun.me/2020/03/31/a-simple-way-to-show-stack-trace-on-error-in-r/:
options(error = function() {
sink(stderr())
on.exit(sink(NULL))
traceback(3, max.lines = 1L)
if (!interactive()) {
q(status = 1)
}
})
mtcars[-title,]
# Error in -title : invalid argument to unary operator
# 2: `[.data.frame`(mtcars, -title, )
# 1: mtcars[-title, ]
In which case it tells you a little more. If it's in a function, that stack trace gives you the line number.
myfunc <- function(title) {
1+1 # doing something
2*2 # doing something else
3^3 # yawn
mtcars[-title,]
}
myfunc(1:30)
# mpg cyl disp hp drat wt qsec vs am gear carb
# Maserati Bora 15.0 8 301 335 3.54 3.57 14.6 0 1 5 8
# Volvo 142E 21.4 4 121 109 4.11 2.78 18.6 1 1 4 2
myfunc(c())
# Error in -title : invalid argument to unary operator
# 3: `[.data.frame`(mtcars, -title, ) at #5
# 2: mtcars[-title, ] at #5
# 1: myfunc(c())
(I know, title is mis-named here, just over-proving the point.)
(Just to assert again: I demonstrated on a data.frame, but this works with vectors/lists as well: (1:10)[-title])
Further, upon seeing your "script": it is not a script. It is a document. If I'm correct, then you are calling this something like Rscript /path/to/file.Rmd. In that case, R thinks this is an R script file, not an R-markdown file.
Let's try this on the console. Copy the following (newline and all) and paste it into your R console:
---
title: "EXAMPLECODE"
When you see the "unary" error, you'll realize that R is interpreting this as a command. In a literal sense, R sees this as: "negate negate negate (newline/whitespace ignored) symbol(title) sequence-colon string(EXAMPLECODE)". (In)Conveniently, title is also a base function in R, so it exists; if it were instead
---
mytitle: "EXAMPLECODE"
(which is not valid Rmd), then your error would have instead read
Error: object 'mytitle' not found
which would have been slightly more clear/informative.
So ultimately I don't know for sure, but my guess is that you are inadvertently telling R to try to interpret the whole thing as an R script, which it is not. Perhaps Rscript knitr::knit("/path/to/file.Rmd") or similar will work instead.

Answer 2

In case someone else gets here, I scratched my head over this error for a ridiculously long time before I realized that I'd coded all the assignment operators in the script as '<--'. I guess I got confused by some software's use of that as a shortcut to an arrow.
Should be -- obvious, I know, but I just have to say it: '<-'