I would like to know if there is an R function that allows to prevent some lines of the code to be executed.
For instance, if this function exist and is called prevent, I could put on my code at line number 10 :
prevent(line12, line17)
and those line wouldn't be executed.
The application for me would pe to prevent some line which are in a loop to be executed, if a condition that I would test before going in the loop is not satisfyed.
It's a matter of optimization : I could test the condition inside the loop but I would rather test it before, since I already know wheter the condition is true or not.
Here is an example :
Condition=T
if (Condition){
Dont execute line 17
}
for (i in 1:n){
line 17 Print("I'm happy")
}
You could simply use an if statement:
condition <- T
for (i in 1:3) {
if (condition) {
cat("Execute this \n")
}
}
you could just add an "#" before the code line you don't want to execute
# 2+2
2+2
You can do it for multiple lines with cmd+shift+c in studio in mac, there should be an Linux or windows equivalent
Have a fully working R-script. When executing it from Rscript it doesn't stop to accept user input however.
The user input is some readline statements. The cat statements prompting for input works as intended. Have I missed something?
I execute 'Rscript scriptfile.R' from terminal on macOS.
You can create a function typeline() to read an input line and then use the result for your next commands. It will wait for your input text either you run your code in Rstudio or in terminal:
typeline <- function(msg="Enter text: ") {
if (interactive() ) {
txt <- readline(msg)
} else {
cat(msg);
txt <- readLines("stdin",n=1);
}
return(txt)
}
txt=typeline("your message: ")
print(txt)
Managed to get it to work by changing readline to readLines as mentioned in the post suggested by meenaparam. The downside with this method is that ithe script only works in batch mode, running it in Rstudio makes it hang. Would be good to know a general way to capture keyboard input i.e that works both in interactive and batch mode.
Use this
cat("What's your name? ")
name <- readLines(file("stdin"),1)
cat("What's your age? ")
age <- readLines(file("stdin"),1)
print(name)
print(age)
Consider this code:
{
cat("hello")
Sys.sleep(1)
cat("\rhi there!")
}
In both the terminal and Rstudio we see the word 'hello' followed by 'hi there!' one second later but the terminal ends with hi there!> while Rstudio ends on a new line with >. Is there any way to get both systems to agree on how they print things using some option? Or is this something special that Rstudio does?
Try with
{
cat("hello")
Sys.sleep(1)
cat("\rhi there!\n")
}
I have looked at other posts that appeared similar to this question but they have not helped me. This may be just my ignorance of R. Thus I decided to sign up and make my first post on stack-overflow.
I am running an R-script and would like the user to decide either to use one of the two following loops. The code to decide user input looks similar to the one below:
#Define the function
method.choice<-function() {
Method.to.use<-readline("Please enter 'New' for new method and'Old' for old method: ")
while(Method.to.use!="New" && Method.to.use!="Old"){ #Make sure selection is one of two inputs
cat("You have not entered a valid input, try again", "\n")
Method.to.use<-readline("Please enter 'New' for new method and 'Old' for old method: ")
cat("You have selected", Method.to.use, "\n")
}
return(Method.to.use)
}
#Run the function
method.choice()
Then below this I have the two possible choices:
if(Method.to.use=="New") {
for(i in 1:nrow(linelist)){...}
}
if(Method.to.use=="Old"){
for(i in 1:nrow(linelist)){...}
}
My issue is, and what I have read from other posts, is that whether I use "readline", "scan" or "ask", R does not wait for my input. Instead R will use the following lines as the input.
The only way I found that R would pause for input is if the code is all on the same line or if it is run line by line (instead of selecting all the code at once). See example from gtools using "ask":
silly <- function()
{
age <- ask("How old are you? ")
age <- as.numeric(age)
cat("In 10 years you will be", age+10, "years old!\n")
}
This runs with a pause:
silly(); paste("this is quite silly")
This does not wait for input:
silly()
paste("this is quite silly")
Any guidance would be appreciated to ensure I can still run my entire script and have it pause at readline without continuing. I am using R-studio and I have checked that interactive==TRUE.
The only other work-around I found is wrapping my entire script into one main function, which is not ideal for me. This may require me to use <<- to write to my environment.
Thank you in advance.
I (sort of) already know the answer to this question. But I figured it is one that gets asked so frequently on the R Users list, that there should be one solid good answer. To the best of my knowledge there is no multiline comment functionality in R. So, does anyone have any good workarounds?
While quite a bit of work in R usually involves interactive sessions (which casts doubt on the need for multiline comments), there are times when I've had to send scripts to colleagues and classmates, much of which involves nontrivial blocks of code. And for people coming from other languages it is a fairly natural question.
In the past I've used quotes. Since strings support linebreaks, running an R script with
"
Here's my multiline comment.
"
a <- 10
rocknroll.lm <- lm(blah blah blah)
...
works fine. Does anyone have a better solution?
You can do this easily in RStudio:
select the code and click CTR+SHIFT+C
to comment/uncomment code.
This does come up on the mailing list fairly regularly, see for example this recent thread on r-help. The consensus answer usually is the one shown above: that given that the language has no direct support, you have to either
work with an editor that has region-to-comment commands, and most advanced R editors do
use the if (FALSE) constructs suggested earlier but note that it still requires complete parsing and must hence be syntactically correct
A neat trick for RStudio I've just discovered is to use #' as this creates an self-expanding comment section (when you return to new line from such a line or insert new lines into such a section it is automatically comment).
[Update] Based on comments.
# An empty function for Comments
Comment <- function(`#Comments`) {invisible()}
#### Comments ####
Comment( `
# Put anything in here except back-ticks.
api_idea <- function() {
return TRUE
}
# Just to show api_idea isn't really there...
print( api_idea )
`)
####
#### Code. ####
foo <- function() {
print( "The above did not evaluate!")
}
foo()
[Original Answer]
Here's another way... check out the pic at the bottom. Cut and paste the code block into RStudio.
Multiline comments that make using an IDE more effective are a "Good Thing", most IDEs or simple editors don't have highlighting of text within simple commented -out blocks; though some authors have taken the time to ensure parsing within here-strings. With R we don't have multi-line comments or here-strings either, but using invisible expressions in RStudio gives all that goodness.
As long as there aren't any backticks in the section desired to be used for a multiline comments, here-strings, or non-executed comment blocks then this might be something worth-while.
#### Intro Notes & Comments ####
invisible( expression( `
{ <= put the brace here to reset the auto indenting...
Base <- function()
{ <^~~~~~~~~~~~~~~~ Use the function as a header and nesting marker for the comments
that show up in the jump-menu.
--->8---
}
External <- function()
{
If we used a function similar to:
api_idea <- function() {
some_api_example <- function( nested ) {
stopifnot( some required check here )
}
print("Cut and paste this into RStudio to see the code-chunk quick-jump structure.")
return converted object
}
#### Code. ####
^~~~~~~~~~~~~~~~~~~~~~~~~~ <= Notice that this comment section isnt in the jump menu!
Putting an apostrophe in isn't causes RStudio to parse as text
and needs to be matched prior to nested structure working again.
api_idea2 <- function() {
} # That isn't in the jump-menu, but the one below is...
api_idea3 <- function() {
}
}
# Just to show api_idea isn't really there...
print( api_idea )
}`) )
####
#### Code. ####
foo <- function() {
print( "The above did not evaluate and cause an error!")
}
foo()
## [1] "The above did not evaluate and cause an error!"
And here's the pic...
I can think of two options. The first option is to use an editor that allows to block comment and uncomment (eg. Eclipse). The second option is to use an if statement. But that will only allow you to 'comment' correct R syntax. Hence a good editor is the prefered workaround.
if(FALSE){
#everything in this case is not executed
}
If find it incredible that any language would not cater for this.
This is probably the cleanest workaround:
anything="
first comment line
second comment line
"
Apart from using the overkilled way to comment multi-line codes just by installing RStudio, you can use Notepad++ as it supports the syntax highlighting of R
(Select multi-lines) -> Edit -> Comment/Uncomment -> Toggle Block Comment
Note that you need to save the code as a .R source first (highlighted in red)
I use vim to edit the R script.
Let's say the R script is test.R, containing say "Line 1", "Line 2", and "Line 3" on 3 separate lines.
I open test.R on the command line with Vim by typing "vim test.R".
Then I go to the 1st line I want to comment out, type "Control-V", down arrow to the last line I want to comment out, type a capital I i.e. "I" for insert, type "# ", and then hit the Escape key to add "# " to every line that I selected by arrowing down. Save the file in Vim and then exit Vim by typing ":wq". Changes should show up in Rstudio.
To delete the comments in Vim, start at the first line on top of the character "#" you want to delete, again do "Control-V", and arrow down to the last line you want to delete a "#" from. Then type "dd". The "#" signs should be deleted.
There's seconds-worth of lag time between when changes to test.R in Vim are reflected in Rstudio.
Now there is a workaround, by using package ARTofR or bannerCommenter
Examples here:
In RStudio an easy way to do this is to write your comment and once you have used CTRL + Shift + C to comment your line of code, then use CTRL + SHIFT + / to reflow you comment onto multiple lines for ease of reading.
In RStudio you can use a pound sign and quote like this:
#' This is a comment
Now, every time you hit return you don't need to add the #', RStudio will automatically put that in for you.
Incidentally, for adding parameters and items that are returned, for standardization if you type an # symbol inside those comment strings, RStudio will automatically show you a list of codes associated with those comment parameters:
#' #param tracker_df Dataframe of limit names and limits
#' #param invoice_data Dataframe of invoice data
#' #return return_list List of scores for each limit and rejected invoice rows