I am not exactly sure what to change in my r code to remove the unexpected symbol.
Error: unexpected symbol in "LP=function(n1,n2,m2){N_hat_LP=(((n1)*(n2))/m2) return(N_hat_LP)}"
The problem is that you have the return command on the same line as the defining of N_hat_LP.
You could put the return(N_hat_LP) command on the next line.
In fact, you can simplify this greatly to just:
LP=function(n1,n2,m2){((n1)*(n2))/m2}
There's no point in defining N_hat_LP just to return it. R understands if you simply include what you want to do with the parameters.
You need to format your code. To prevent this, I recomment to read a style guide http://r-pkgs.had.co.nz/style.html. To solve the error, you can reformat:
LP <- function(n1, n2, m2) {
N_hat_LP <- n1 * n2 / m2
return(N_hat_LP)
}
Or leaf it in one line:
LP=function(n1,n2,m2){N_hat_LP=(((n1)*(n2))/m2);return(N_hat_LP)}
Related
I want to print every argument passed to function read.table. My idea was to write some decorator that is easy in Python. But for R, I don't know how to do it, what I learned was to use trace(). However, I don't know how to print variables inside trace.
Example:
trace(f)
a <- "123"
f(a)
untrace(f)
trace() will only output f(a), but I want to know the evaluation of a.
thanks for your guys' help, I find the answer.
Simply use the following code:
trace(f, tracer = quote(print(lapply(as.list(match.call()),eval))))
d<-1
f(d)
untrace(f)
I am attempting to replace if with if( using GNU m4 1.4.14 and I am receiving ERROR: end of file in argument list
when trying:
define(`if', `if(')
define(`then', `){')
define(`fi', `}')
if foo then bar() fi
I have tried escaping the parentheses but that caused m4 to error after a brief period of time saying it's out of memory. Scanning through the manual, I found nothing related to this problem.
Upon changing the name of the macro to 'IF' or something other than 'if', it works as expected, which leads me to believe it's evaluating itself repeatedly.
If so, how can I define a macro that is evaluated only once? Otherwise, what should I look into to fix this?
EDIT I found a way around this issue by processing twice, once to convert if to _IF and the next to convert _IF to if(. I assume there's a better way to do this, so this is only a temporary solution in my eyes.
You need to prevent m4 from attempting to re-expanding the replacements. Do so by double quoting:
define(`if', ``if('')
define(`then', `){')
define(`fi', `}')
if foo then bar() fi
Sometimes R throws me errors such as
Error in if (ncol(x) != 2) { : argument is of length zero
with no additional information, when I've written no such code. Is there a general way for finding which function in which package causes an error?
Since most packages come compressed, it isn't trivial to grep /usr/lib/R/library.
You can use traceback() to locate where the last error occurred. Usually it will point you to a call you make in your function. Then I typically put browser() at that point, run the function again and see what is going wrong.
For example, here are two functions:
f2 <- function(x)
{
if (x==1) "foo"
}
f <- function(x)
{
f2(x)
}
Note that f2() assumes an argument of length 1. We can misuse f:
> f(NULL)
Error in if (x == 1) "foo" : argument is of length zero
Now we can use traceback() to locate what went wrong:
> traceback()
2: f2(x) at #3
1: f(NULL)
The number means how deep we are in the nested functions. So we see that f calls f2 and that gives an error at line 3. Pretty clear. We could reassign f with browser placed just before the f2 call now to check it's input. browser() simply allows you to stop executing a function and look around in its environment. Similar to debug and debugonce except that you don't have to execute every line up until the point you know something goes wrong.
Just to add to what #SachaEpskamp has already suggested, setting options(error=recover) and options(show.error.locations=TRUE) can be extremely helpful when debugging unfamiliar code. The first causes R to launch a debugging session on error, giving you the option to invoke the browser at any point in the call stack up to that error. The second option will tell R to include the source line number in the error.
I have problem in using if else inside function, my code is like this:
ConvertWgtZooLS <- function(WgtZoo, LSWay, Pos){
If(LSWay == 0){
NewWgtZoo <- WgtZoo
}else{
BackPos <- BackMatrix(Pos,1)
NewWgtZoo<- Ifelse((Sign(WgtZoo) * Sign(BackPos) * LSWay)>=0, WgtZoo, 0)
}
return(NewWgtZoo)
}
However, when I run that in R, error message appears as:
"Error: unexpected '{' in:
"ConvertWgtZooLS <- function(WgtZoo, LSWay, Pos){
If(LSWay == 0){"
How can I resolve this? What is the syntax problem there? I checked many websites and seems the above if else syntax is correct.
Thanks a lot!
The error in your code is that you have used If instead of if, and R is case-sensitive. Thus, it is possible to have another function named If that does something different from if, and, as #danielkullmann points out, that function is exactly what R is looking for.
The error messages that R produces are not always the most helpful, but in this case, it does point you very close to the problem area. It shows you where it got "confused" but it's up to you to figure out why!
After you've fixed that first problem, you'll find another one (for the same reason) on line 6, where you have written Ifelse instead of ifelse.
One last point: R is pretty whitespace friendly, so it is good practice to leave some space in your code to help improve legibility, particularly with if and else statements. Here's why:
I find if (LSWay == 0) { easier to read than if(LSWay == 0){
When using an actual function, like sum(x), you do not usually add a space, making it easier to spot these conditional statements in large blocks of code.
The Google R Style Guide is an interesting read in this regard.
I have written an R script which includes a loop that retrieves external (web) data. The format of the data are most of the time the same, however sometimes the format changes in an unpredictable way and my loop is crashing (stops running).
Is there a way to continue code execution regardless the error? I am looking for something similar to "On error Resume Next" from VBA.
Thank you in advance.
Use try or tryCatch.
for(i in something)
{
res <- try(expression_to_get_data)
if(inherits(res, "try-error"))
{
#error handling code, maybe just skip this iteration using
next
}
#rest of iteration for case of no error
}
The modern way to do this uses purrr::possibly.
First, write a function that gets your data, get_data().
Then modify the function to return a default value in the case of an error.
get_data2 <- possibly(get_data, otherwise = NA)
Now call the modified function in the loop.
for(i in something) {
res <- get_data2(i)
}
You can use try:
# a has not been defined
for(i in 1:3)
{
if(i==2) try(print(a),silent=TRUE)
else print(i)
}
How about these solutions on this related question :
Is there a way to `source()` and continue after an error?
Either parse(file = "script.R") followed by a loop'd try(eval()) on each expression in the result.
Or the evaluate package.
If all you need to do is a small piece of clean up, then on.exit() may be the simplest option. It will execute the expression "when the current function exits (either naturally or as the result of an error)" (documentation here).
For example, the following will delete my_large_dataframe regardless of whether output_to_save gets created.
on.exit(rm("my_large_dataframe"))
my_large_dataframe = function_that_does_not_error()
output_to_save = function_that_does_error(my_large_dataframe)