如何将函数应用于R中的几个变量？

Question

I have a simple/confusing question in R.

Here is an example of my problem.

I have a string of numbers or characters:

data <- c(1,2,3,4,5)

and I have a function which I want to apply to several variables in the string.

dd <- function(d){if(d==data[1:3]) 'yes'
else 'no'}

but when I apply the function to the string I got this error

unlist(lapply(data,dd))

Warning message:

   1: In if (d == data[1:3]) "yes" :
    the condition has length > 1 and only the first element will be used
    2: In if (d == data[1:3]) "yes" :
    the condition has length > 1 and only the first element will be used
    3: In if (d == data[1:3]) "yes" :
    the condition has length > 1 and only the first element will be used
   4: In if (d == data[1:3]) "yes" :
  the condition has length > 1 and only the first element will be used
   5: In if (d == data[1:3]) "yes" :
  the condition has length > 1 and only the first element will be used

So, My question is how can I apply the function to several variables in the string not just for the first element? to get an output like

"yes" "yes" "yes" "no" "no"

Thanks in Advance,

Answer 1

There is no need for a lapply loop. You can use the vectorized ifelse and need to use %in% : ifelse(d %in% data[1:3], "yes", "no")

Answering the follow-up question in your comment:

It works but how can I apply this to for example: if I want to have 'yes' for c(1,2) and 'no' for '3' and 'None' to the rest (4,5)?

There are several ways to achieve that. You could use a nested ifelse . However, in the specific example I would use cut :

cut(data, breaks = c(-Inf, 2, 3, Inf), labels = c("yes", "no", "None"))
#[1] yes  yes  no   None None
#Levels: yes no None