I should correct unfinished function Rfun() but I haven't managed to find all of the problems.
Rfun(N){
A=matrix(0,nrow=50,ncol=300)
t=c(0:30,0:-30)
for(j in 1:50)
x=N[j,]
y=cumsum(x)
for(i in 1:300){
A[j,i]=y[i]/3
}
}
return(A)
}
Well since you didn't precise what the function should do, let me help you with what is apparently false to me:
This is not how you define a function in R you need to write Rfun = function(N){}.
The return(A) should be inside the function. Therefore you should remove one parenthesis.
the variable t is not used at all.
Related
I recently study R, but I am not familiar with using the function. I was trying to use a function to modify my initial input like:
x<-c(1,2,3,4,5,5,4)
number_to_words<-function(x){
a<-1
while(a<8){
if(x[a]==1){
as.character(x[a])
x[a]<-"one"
}
else if(x[a]==2){
as.character(x[a])
x[a]<-"two"
}
else if(x[a]==3){
as.character(x[a])
x[a]<-"three"
}
else{
as.character(x[a])
x[a]<-"four"
}
a=a+1
}
return(x)
}
number_to_words(x)
x
but I found out that the value in x hadn't been changed, whether there is a method that I could let each component of x[a] in my function to be modified and stored? like x->f(x)->y but x's value is replaced by y?
The issue you have here is that you are assuming that the function is "call by reference" but R uses "call by value". This basically means that a copy of the arguments you pass into a function is made and it is that copy that you are manipulating inside the function.
The easiest solution in your case is to overwrite x when your function returns
x <- number_to_words(x)
Goal
I am trying to create a function in R to replicate the functionality of a homonymous MATLAB function which returns the number of arguments that were passed to a function.
Example
Consider the function below:
addme <- function(a, b) {
if (nargin() == 2) {
c <- a + b
} else if (nargin() == 1) {
c <- a + a
} else {
c <- 0
}
return(c)
}
Once the user runs addme(), I want nargin() to basically look at how many parameters were passed―2 (a and b), only 1 (a) or none―and calculate c accordingly.
What I have tried
After spending a lot of time messing around with environments, this is the closest I ever got to a working solution:
nargin <- function() {
length(as.list(match.call(envir = parent.env(environment()))))
}
The problem with this function is that it always returns 0, and the reason why is that I think it's looking at its own environment instead of its parent's (in spite of my attempt of throwing in a parent.env there).
I know I can use missing() and args() inside addme() to achieve the same functionality, but I'll be needing this quite a few other times throughout my project, so wrapping it in a function is definitely something I should try to do.
Question
How can I get nargin() to return the number of arguments that were passed to its parent function?
You could use
nargin <- function() {
if(sys.nframe()<2) stop("must be called from inside a function")
length(as.list(sys.call(-1)))-1
}
Basically you just use sys.call(-1) to go up the call stack to the calling function and get it's call and then count the number of elements and subtract one for the function name itself.
I have a package which provides a script and some functions. Within the script I assign a variable which will be used by the function. This works if the function gets executed within the script but might fail if I just call the function since the variable doesn't exist.
If I use devtools::check() I get warnings, that the variable within the function isn't defined. How can I handle this properly?
Edit
I am thinking about to use get() within the function to assign the variable within the function to get rid of this warnings. So the question is, is myp2 the correct way of doing something like this? Maybe some trycatch to handle errors?
ab <- c(1,2,3)
myp1 <- function() {
print(ab)
return(1)
}
myp2 <- function() {
ab <- get('ab')
print(ab)
return(1)
}
myp1()
myp2()
You could do something like
if(!exists("your variable")){
stop("You have not defined your variable")}
This would check to see if what you are looking for exists. A better practice would be to define the variable in the function and have the default value be the name of the thing for which you are looking.
myp <- function(x) {
print(x)
return(1)
}
ab <- c(1,2,3)
myp(x = ab)
If possible, it would be also better to substitute the script with a function.
can please somebody tell me how I can call my output which are two matrices as an input into another function?
X1=function(y,z)
{
output1=y*z
output2=y/z
}
X2=function(p,q)
{
input=X1(y,z)
input1=input$output1 ??? How to specify the output that I can call it this way? output1 and output2 are matrices!
input2=input$output2
equation=input1+input2
}
I tried return() and data.frame but both didn't work. Any tipps?
You can't use c as some might otherwise expect because you'll lose the structure of the matrices. Instead, use list when you want to return multiple objects from an R function.
X1 <- function(y,z)
{
list(
output1=y*z,
output2=y/z
)
}
based on Roland's suggestion from Plot titles in R using sapply(), I have created the following loop to make boxplots out of every selected variable in my dataset.
all.box=function(x) {
for (i in seq_along(x)) {
boxplot(x[,i], main = names(x)[i])
}
}
It does the job nicely in that it provides the graphs. Could someone point out to me how to make the loop to return some output, say the $out from the boxplot to be able to see the number of outliers calculated by it?
Thanx a lot!
Using lapply here is better to avoid side-effect of the for:
all.box=function(x) {
res <- lapply(seq_along(x),function(i){
boxplot(x[,i], main = names(x)[i])$out
})
res
}
PS: you can continue to use for, but you will need either to append a list as a result within your loop or to allocate memory for the output object before calling boxplot. So I think it is simpler to use xxapply family function here.
If you want to return something from a for loop, it's very important to pre-allocate the return object if it's not a list. Otherwise for loops with many iterations will be slow. I suggest to read the R inferno and Circle 2 in particular.
all.box=function(x) {
result <- list()
for (i in seq_along(x)) {
result[[i]] <- boxplot(x[,i], main = names(x)[i])$out
}
result
}