R if else 代码将两个变量合二为一

Question

I have two variables - Small_Vehicle and Large_Vehicle which are coded as 0 and 1s. I want to combine them into one variable where if the vehicle was small - 1, and if it was large - 2. If there is no data, I want R to leave is as NA. I have written the code below but it gives me the error:

Error: unexpected '}' in " TRIdata$Combined <- NA }"

The Combined variable already exists in the dataset but has the wrong values currently.

if (TRIdata$Small_Vehicle = 1) {
TRIdata$Combined<-1 } else {
if (TRIdata$Large_Vehicle=1)  {
TRIdata$Combined<-2 } else {
TRIdata$Combined <- NA }}

Do you have any suggestions about what I am doing wrong, please?

Thank you!

Answer 1

Assuming that small_vehicle and large_vehicle are mutually exclusive and exhaustive categories, we can create Combined without if / then logic as follows.

small_vehicle <- c(1,0,0,1,1,1,0)
large_vehicle <- c(0,1,1,0,0,0,1)

TRIdata <- data.frame(small_vehicle,large_vehicle)
TRIdata$Combined <- 2*TRIdata$large_vehicle + small_vehicle

TRIdata

...and the output:

> TRIdata
  small_vehicle large_vehicle Combined
1             1             0        1
2             0             1        2
3             0             1        2
4             1             0        1
5             1             0        1
6             1             0        1
7             0             1        2
> 

Alternate approach

We can do the same thing with ifelse() .

# alternate approach 
small_vehicle <- c(1,0,0,1,1,1,0)
large_vehicle <- c(0,1,1,0,0,0,1)

TRIdata <- data.frame(small_vehicle,large_vehicle)
TRIdata$Combined <- ifelse(TRIdata$small_vehicle == 1,1,2)
TRIdata

...and the output.

> TRIdata
  small_vehicle large_vehicle Combined
1             1             0        1
2             0             1        2
3             0             1        2
4             1             0        1
5             1             0        1
6             1             0        1
7             0             1        2
> 

Why doesn't the original code work?

I'll illustrate my comment on the original post with the following code. We'll correct the = vs. == error in the original, and then attempt to run it.

# original code with my sample data
small_vehicle <- c(1,0,0,1,1,1,0)
large_vehicle <- c(0,1,1,0,0,0,1)
TRIdata <- data.frame(Small_Vehicle = small_vehicle,
                      Large_Vehicle = large_vehicle)

if (TRIdata$Small_Vehicle == 1) {
     TRIdata$Combined <- 1
} else {
     if (TRIdata$Large_Vehicle == 1)  {
          TRIdata$Combined <- 2
     } else {
          TRIdata$Combined <- NA
     }
}

...produces the following warning:

Warning message:
In if (TRIdata$Small_Vehicle == 1) { :
  the condition has length > 1 and only the first element will be used
> 

When we print the results, we observe that R evaluated the first element of TRIdata$Small_Vehicle as TRUE, and assigned the value of 1 to every element in TRIdata$Combined .

> TRIdata
  Small_Vehicle Large_Vehicle Combined
1             1             0        1
2             0             1        1
3             0             1        1
4             1             0        1
5             1             0        1
6             1             0        1
7             0             1        1
>

Answer 2

Try this.

if (TRIdata$Small_Vehicle == 1) {
    TRIdata$Combined<-1 } elseif (TRIdata$Large_Vehicle=1) {
    TRIdata$Combined<-2 } else {
    TRIdata$Combined <- NA }