I'm trying to use multiple actions in if statement. For example:
x <- 1
if (x == 1) {
paste("First")
1*1 #multiple actions
} else if (x == 2) {
paste("Second")
2*2 } else {("Nothing")
}
[1] 1 #what I'm getting
[2] "First"
1 #what I want to get
In this case only the second part of the expressions was printed to the console.
Any ideas how can I run all actions between if and else if ?
All statements are running as intended. The value of a statement is only printed to the console if all these conditions are true:
The value isn't saved to a variable
The value isn't invisible
It's the result of the last statement in an expression
R is running in interactive mode
The reason things sometimes print is to help people interactively exploring data in the command line. Instead of type print(x), they can save a few keystrokes by just typing x. In summary, use print if you want to be sure it's printed:
x <- 1
if (x == 1) {
print("First")
print(1*1)
} else if (x == 2) {
print("Second")
print(2*2)
} else {
invisible("Nothing")
}
# [1] "First"
# [1] 1
You can use print or cat:
getResult <- function(x = 1) {
if (x == 1) {
cat("First", 1 * 1, "\n")
} else if (x == 2) {
print("Second")
print(2 * 2)
} else {
cat("Nothing\n")
}
}
getResult()
# First 1
getResult(2)
# [1] "Second"
# [1] 4
Related
It is clearly that the documentation of R clearly goes against having a break line between "}" and "else". However, it is odd that the first piece of codes works but the second one does not work (syntax error)
First program
x = 1
stupid_function = function(x){
if(x != 1){
print("haha")
}
else if( x == 1){
print("hihi")
}
}
stupid_function(x)
[1] "hihi"
Second program
x = 1
if(x != 1){
print("haha")
}
else if( x == 1){
print("hihi")
}
Error in source("~/.active-rstudio-document", echo = TRUE) :
~/.active-rstudio-document:6:3: unexpected 'else'
5: }
6: else
In the second program it sees a line at a time as it is typed in so at the point that the line with the } is typed in it cannot know that there will be further lines with an else so it assumes the statement is finished.
In the first case it can see all the code before it is run because it can see all the code in the function so it knows that the } has not finished the statement.
This line of argument works for an if/else but does not work in general. For example, this will produce an error when the function is
defined.
f <- function(x) {
x
* 2
}
Note that the if else need not be in a function for it to work. It just need to be in a continuous form or in a way to be expressed as a continuous block of code. One way is being in a function. The other is to write it in one line, or even ensure that there is no line break between the if block and the else block:
x <- 1
if(x != 1) print('haha') else print('hihi')
[1] "hihi"
More blocks of statements:
x <- 1
if(x != 1){
print("haha")
} else if( x == 1){ # Note how else begins immediatley after }
print("hihi")
}
[1] "hihi"
Note that you need to know when to put the line breaks whether in a function or outside of a function. Otherwise the code might fail or even give incorrect results.
Using subtraction:
x <- 1
x -
2
[1] -1
x <- 1
x
- 2
[1] -2
You need to know when/where to have the line breaks. Its always safe to have else follow the closing brace } of the previous if statement. ie:
if(...){
....
} else if(...){
....
} else {
...
}
I'm working with panel data in R and am endeavoring to build a function that returns every user ID where PCA==1. I've largely gotten this to work, with one small problem: it only returns the values when I end the function with print() but does not do so when I end the function with return(). As I want the ids in a vector so I can later subset the data to only include those IDs, that's a problem. Code reflected below - can anyone advise on what I'm doing wrong?
The version that works (but doesn't do what I want):
retrievePCA<-function(data) {
for (i in 1:dim(data)[1]) {
if (data$PCA[i] == 1) {
id<-data$CPSIDP[i]
print(id)
}
}
}
retrievePCA(data)
The version that doesn't:
retrievePCA<-function(data) {
for (i in 1:dim(data)[1]) {
if (data$PCA[i] == 1) {
id<-data$CPSIDP[i]
return(id)
}
}
}
vector<-retrievePCA(data)
vector
Your problem is a simple misunderstanding of what a function and returning from a function does.
Take the small example below
f <- function(x){
x <- x * x
return x
x <- x * x
return x
}
f(2)
[1] 4
4 is returned, 8 is not. That is because return exits the function returning the specific value. So in your function the function hits the first instance where PCA[i] == 1 and then exits the function. Instead you should create a vector, list or another alternative and return this instead.
retrievePCA<-function(data) {
ids <- vector('list', nrow(data))
for (i in 1:nrow(data)) {
if (data$PCA[i] == 1) {
ids[[i]] <-data$CPSIDP[i]
}
}
return unlist(ids)
}
However you could just do this in one line
data$CPSIDP[data$PCA == 1]
enter image description here
I know there exists function 'unique' which works similar to what I want to make, but I want to make this function.
I want this function finally returns 'result' which contains unique elements of input vector.
But I don't know why this function's result is totally different from my expect.
Why c which is to combine before result and new unique element is not working.
Please tell me how to fix my code.
Thank you.
I think what you expect might be something like below, where result should be an argument of m_uni:
m_uni <- function(x,result = c()) {
if (class(x)=='numeric'| class(x)=='character') {
if (length(x) <= 1){
return(result)
} else {
if (x[length(x)] %in% result) {
x <- x[-length(x)]
m_uni(x,result)
} else {
result <- c(result,x[length(x)])
x <- x[-length(x)]
m_uni(x,result)
}
}
} else {
return('This function only gets numeric or character vector')
}
}
such that
> m_uni(x)
[1] 0 4 5 -2
This is a very common question: 1, 2, 3, 4, 5, and still I cannot find even an answer to my problem.
If a == 1, then do X.
If a == 0, then do Y.
If a == 0 and b == 1, then do Z.
Just to explain: the if else statements has to do Y if a==0 no matter the value of b. But if b == 1 and a == 0, Z will do additional changes to those already done by Y.
My current code and its error:
if (a == 1){
X
} else if(a == 0){
Y
} else if (a == 0 & b == 1){
Z}
Error in !criterion : invalid argument type
An else only happens if a previous if hasn't happened.
When you say
But if b == 1 and a == 0, Z will do additional changes to those already done by Y
Then you have two options:
## Option 1: nest Z inside Y
if (a == 1){
X
} else if(a == 0){
Y
if (b == 1){
Z
}
}
## Option 2: just use `if` again (not `else if`):
if (a == 1) {
X
} else if(a == 0) {
Y
}
if (a == 0 & b == 1) {
Z
}
Really, you don't need any else here at all.
## This will work just as well
## (assuming that `X` can't change the value of a from 1 to 0
if (a == 1) {
X
}
if (a == 0) {
Y
if (b == 1){
Z
}
}
Typically else is needed when you want to have a "final" action that is done only if none of the previous if options were used, for example:
# try to guess my number between 1 and 10
if (your_guess == 8) {
print("Congratulations, you guessed my number!")
} else if (your_guess == 7 | your_guess = 9) {
print("Close, but not quite")
} else {
print("Wrong. Not even close!")
}
In the above, else is useful because I don't want to have enumerate all the other possible guesses (or even bad inputs) that a user might enter. If they guess 8, they win. If they guess 7 or 9, I tell them they were close. Anything else, no matter what it is, I just say "wrong".
Note: this is true for programming languages in general. It is not unique to R.
However, since this is in the R tag, I should mention that R has if{}else{} and ifelse(), and they are different.
if{} (and optionally else{}) evaluates a single condition, and you can run code to do anything in {} depending on that condition.
ifelse() is a vectorized function, it's arguments are test, yes, no. The test evaluates to a boolean vector of TRUE and FALSE values. The yes and no arguments must be vectors of the same length as test. The result will be a vector of the same length as test, with the corresponding values of yes (when test is TRUE) and no (when test is FALSE).
I believe you want to include Z in the second condition like this:
if (a == 1){X}
else if(a == 0){
Y
if (b == 1){Z}
}
I know that in Java it is often quite handy to do things like that
if(a!=0 && b/a>1){
...;
}
Java stops when the first part is already false. R does not do that, producing errors sometimes. So: Is there a possibility to make this code shorter:
if(exists("user_set_variable")){
if(user_set_variable < 3){
...
}
}
R also short-circuits the && and || operators when the second argument doesn't need to be evaluated. For example (here x does not exist)
> if (exists('x') && x < 3) { print('do this') } else { print ('do that') }
[1] "do that"
From ?'&&' you can find
& and && indicate logical AND and | and || indicate logical OR.
The shorter form performs elementwise comparisons in much the same
way as arithmetic operators. The longer form evaluates left to right
examining only the first element of each vector. Evaluation proceeds
only until the result is determined. The longer form is appropriate
for programming control-flow and typically preferred in if clauses.
So probably you're looking for & instead of &&. See these examples where two conditions are evaluated:
# Case 1
a<- 2
b <- 4
if(a!=0 & b/a>1){
print('Hello World')
} else{
print("one or both conditions not met")
}
[1] "Hello World"
# Case 2
a<- 2
b <- 1
if(a!=0 & b/a>1){
print('Hello World')
} else{
print("one or both conditions not met")
}
[1] "one or both conditions not met"
# Case 3
a<- 0
b <- 1
if(a!=0 & b/a>1){
print('Hello World')
} else{
print("one or both conditions not met")
}
[1] "one or both conditions not met"
Either use the short-circuit statements if those are clear enough as they are or you could just wrap your multiple if statement lines into a function. Here's some pseudo-code for a visual.
if(exists("user_set_variable")){ if(user_set_variable < 3){
... } }
Could then be:
var<- "user_set_variable" 'let var be your variable for this
if(exists(var) && var < 3)
{ 'do stuff }
or do this:
'function definition
Function boolean IsValidVar(variable)
{
if(exists(var))
{
if(var < 3)
{ return true; }}
return false;
}
then your program looks like so:
var<- "user_set_variable" 'let var be your variable for this
if(IsValidVar(var))
{ 'do stuff }
It's really just your call what seems simple.