R：应用dprime函数-apply（）错误'dim（X）必须具有正长度”

Question

I'm trying to write a dprime function where I subtract FA from hits z-scores to get a dprime value for each participant. Participants are rows and z-scores are columns. My dataset (newData) is 18x16 but I want to ignore the first 8 columns. I want to repeat the dprime calculation for each of condition and create a new 18x4 dataset (newData2) with the output.

# Function to apply
dprimeFun <- function(twoColumns){
  # Give the function two columns at a time
  zH <- twoColumns[ 1 ]
  zF <- twoColumns[ 2 ]
  dprime <- zH - zF 
  return(dprime)
}

# Apply the function
newData2 <- cbind(
  # Condition 1 dprimes
  apply(
    newData[ c( "zH1","zF1" ) ], MARGIN=1, FUN=dprimeFun
  ),
  # Repeat for each condition
)

When I run this I get the following error:

Error in apply(newData[c("zH1", "zF1")], MARGIN = 1, FUN = dprimeFun) : 
  dim(X) must have a positive length

I found this question where somebody had the same error message, however I think their solution (just apply the function directly to the data subset) won't work for me because I'd have to do so 72 times.

I also read the R FAQ 'Why do matrices lose dimensions?' but I don't understand how it applies to my 18x16 dataset.

I'm an R newb so help would be much appreciated.

Edit:

# newData structure
> str(newData)
 num [1:18, 1:16] 0.833 0.833 0.833 0.833 0.833 ...
 - attr(*, "dimnames")=List of 2
  ..$ : NULL
  ..$ : chr [1:16] "H1" "F1" "H2" "F2" ...

# newData column names
> colnames(newData)
 [1] "H1"  "F1"  "H2"  "F2"  "H3"  "F3"  "H4"  "F4"  "zH1" "zF1" "zH2" "zF2" "zH3" "zF3"
[15] "zH4" "zF4"

Answer 1

Perhaps you want...

newData$dprime <- dprimeFun(newData[,c("zH1", "zF1")])

But it's extraordinarily hard to tell.