duckduckgoes - 6 months ago 64

R Question

I am new to R. Here is the SAS script that I want to replicate in R:

`if a=4 or b=4 then do;`

if a=1 or b=1 then news="AB";

else if a=2 or b=2 then news="BC";

else news="CD";

end;

else do;

if a=1 or b=1 then news="DF";

else news="GH";

end;

Where: a, b are variables (columns's name) of the table/data, and news is a new variable that I want to create.

I cannot find a way of ifelse or other methods to do that in R. Can you help me? Thank you!

Here is my first try on first part of the above script:

`news <- ifelse(a==4 | b==4,`

ifelse(a==1 | b==1, "AB",

ifelse(a==2 | b==2, "BC", "CD")))

But it did not work. The error shows

"Error in ifelse(a == 4 | b == 4, ifelse(a == 1 | b == :

argument "no" is missing, with no default"

Do you know why? Also, I am not sure how to link the second part, starting from "else do" to R. I feel like SAS script is easier to understand and write in this case than R.

Answer

`ifelse`

is appropriate for vectors (i.e., you must test a vector and the output must be a vector of the same length as the input), `if() {...} else {...}`

is for single conditions. Without sample input (and not really knowing SAS), I'm not sure which you're after. If `a`

and `b`

are single values, R Schifini's answer is good.

If `a`

and `b`

are vectors, then you are right to use `ifelse`

, and your code works just fine for me. We can extend it to include the last `else do`

statement:

```
test = expand.grid(a = c(1, 2, 4, 7), b = c(1, 2, 4))
a = test$a
b = test$b
news <- ifelse(a == 4 | b == 4,
ifelse(a == 1 | b == 1, "AB",
ifelse(a == 2 | b == 2, "BC", "CD")),
ifelse(a == 1 | b == 1, "DF", "GH"))
cbind(test, news)
# a b news
# 1 1 1 DF
# 2 2 1 DF
# 3 4 1 AB
# 4 7 1 DF
# 5 1 2 DF
# 6 2 2 GH
# 7 4 2 BC
# 8 7 2 GH
# 9 1 4 AB
# 10 2 4 BC
# 11 4 4 CD
# 12 7 4 CD
```