R：如何在 if 语句中设置 2 个结果

Question

I want to set 2 Console output in the if statement: one is the paste() function and sencond is unique values from one of the column

if (x<= 0) {
Paste("Negative"),
unique(data$category)
}

Answer 1

You can't return two things at once, but there are couple of ways to output both objects on the console:

1. Assign each object to a variable, and output the variables one at a time
2. Store both objects together in a list, and output the list to the console

1. Assign each value to a different variable

The variables will be stored in the global environment, so they will be accessible subsequent to the execution of the if statement.

x <- -3
data <- data.frame(category = c("foo", "bar", "baz"))

if (x <= 0){
  my.text <- "Negative"
  my.values <- unique(data[["category"]])
}
 
## Now you can do as you please with these variables. For example:

cat("The value of x is", my.text)
#> The value of x is Negative

length(my.values)
#> [1] 3

^{Created on 2022-08-23 by the reprex package (v2.0.1)}

2. Immediately return a two-element list

x <- -3
data <- data.frame(category = c("foo", "bar", "baz"))


if (x <= 0){

  list(
    polarity = "Negative",
    values   = unique(data[["category"]])
  )

}
#> $polarity
#> [1] "Negative"
#> 
#> $values
#> [1] "foo" "bar" "baz"

^{Created on 2022-08-23 by the reprex package (v2.0.1)}

3. Bonus solution: Use cat() to print to the console

If you don't actually want to return the objects, but you just want to print them to the console, you can use cat() . Depending on your aims, you might also consider using message() , which is designed to give messages to the user (or a log).

x <- -3
data <- data.frame(category = c("foo", "bar", "baz"))


if (x <= 0){

  cat("Negative")
  cat(data[["category"]])
  
}
#> Negativefoo bar baz

### or consider:

if (x <= 0){
  
  message("Negative")
  message(data[["category"]])
  
}
#> Negative
#> foobarbaz

^{Created on 2022-08-23 by the reprex package (v2.0.1)}