Replace value in one column into a value from another column

[Mayasak]

I have a large data where I have to replace 'detected' from Organism variable into value from RESULT. I used the following code:
LAB$Organism[psie$Organism == 'DETECT'] <- LAB$RESULT
I got the following error: "NAs are not allowed in subscripted assignments".
I'm still new to R so I have no idea what is missing! Do I have to a code that take care of null values?
Any help is really appreciated.
Thank you

[FJCC]

Is this the sort of thing you are trying to do?

LAB <- data.frame(Organism = c("foo","DETECT",NA,"bar"),
                  RESULT = c("A","B","C","D"))

LAB
#>   Organism RESULT
#> 1      foo      A
#> 2   DETECT      B
#> 3     <NA>      C
#> 4      bar      D
LAB$Organism <- ifelse(LAB$Organism != 'DETECT', LAB$Organism, LAB$RESULT)
LAB
#>   Organism RESULT
#> 1      foo      A
#> 2        B      B
#> 3     <NA>      C
#> 4      bar      D

^{Created on 2023-06-25 with reprex v2.0.2}

It is unusual that you are subsetting the LAB data frame using a column from the psie data frame. That might be correct but you should check if that is what you want to do.

[technocrat]

If the question is asked in those terms to a chatbot, an incorrect answer will be provided. A more careful question, using @FJCC 's data frame returns his result.

LAB <- data.frame(Organism = c("foo","DETECT",NA,"bar"),
                  RESULT = c("A","B","C","D"))
psie <- data.frame(Organism = c("foo","DETECT",NA,"bar"),
                  RESULT = c("A","Z","C","D"))

LAB$RESULT <- ifelse(LAB$Organism == "DETECT" & psie$Organism == "DETECT",
                     psie$RESULT,
                     LAB$RESULT)

LAB
#>   Organism RESULT
#> 1      foo      A
#> 2   DETECT      Z
#> 3     <NA>   <NA>
#> 4      bar      D

^{Created on 2023-06-25 with reprex v2.0.2}

Question posed:
In the R programming language, I have two large data frames that look like these examples

LAB <- data.frame(Organism = c("foo","DETECT",NA,"bar"),
                  RESULT = c("A","B","C","D"))
psie <- data.frame(Organism = c("foo","DETECT",NA,"bar"),
                  RESULT = c("A","B","Z","D"))

Write a script to replace the value of LAB$RESULT with psie$RESULT when the value "DETECT" appears in both LAB$Orgamism and psie$Organism. Asking for guidance on what to do, rather than how to do it or to correct the immediate mistake, is much more effective.