Very New to R. Trying to create a variable

[Kjarman]

Hello, I'm very new to R and need some general help to get started in R studio.

I need to create a new variable called cd4cat defined as 0 if cd4< 100, 1 if cd4 ∈ [100, 199]
and 2 if cd4 ≥ 200. I've been told to literally type in create a new variable named cd4cat and it just got a big red X next to it so any assistance is appreciated. Below is where I'm at so far.

library(speff2trial)
library(survival)
data(ACTG175)

?ACTG175

Then define:

ACTG175$cd4cat[ACTG175@cd40<100]=0
ACTG175$cd4cat[ACTG175@cd40>=100 & ACTG175@cd40<=199]=1
ACTG175$cd4cat[ACTG175@cd40>=200]=2

[technocrat]

@Kjarman

ACTG175$cd4cat[ACTG175@cd40<100]=0
ACTG175$cd4cat[ACTG175@cd40>=100 & ACTG175@cd40<=199]=1
ACTG175$cd4cat[ACTG175@cd40>=200]=2

You got the hard part right.

suppressPackageStartupMessages({
  library(speff2trial)
  library(survival)
})

data(ACTG175)
colnames(ACTG175)
#>  [1] "pidnum"  "age"     "wtkg"    "hemo"    "homo"    "drugs"   "karnof" 
#>  [8] "oprior"  "z30"     "zprior"  "preanti" "race"    "gender"  "str2"   
#> [15] "strat"   "symptom" "treat"   "offtrt"  "cd40"    "cd420"   "cd496"  
#> [22] "r"       "cd80"    "cd820"   "cens"    "days"    "arms"

ACTG175$cd4cat[ACTG175$cd40 < 100] <- 0
ACTG175$cd4cat[ACTG175$cd40 >= 100 & ACTG175$cd40 <= 199] <- 1
ACTG175$cd4cat[ACTG175$cd40 >= 200] <- 2

head(ACTG175["cd4cat"])
#>   cd4cat
#> 1      2
#> 2      1
#> 3      2
#> 4      2
#> 5      2
#> 6      2

but got tripped using the @ operator in place of $

ACTG175$cd4cat[ACTG175@cd40<100]=0
Error in ACTG175$cd4cat[ACTG175@cd40 < 100] = 0 : 
  trying to get slot "cd40" from an object (class "data.frame") that is not an S4 object