Apply acoustic indices to each component of a list of wave objects in R

Question

I am looking to apply a function which computes four acoustic indices (Hf, AEI, ACI and NDSI) to a list of 55 60-second wave objects. I have found code which applies the function to a .wav file, however I'm having difficulty in altering the code to work for each component of a list rather than a .wav file.

This is the code im trying to compute:

#create function to be applied to list of wave objects
indices <- function(x) {
  x <- readWave(x)
  return(c(sh(meanspec(x, plot=FALSE)),
           acoustic_evenness(x) $aei_left,
           ACI(x),
           NDSI(soundscapespec(x, plot=FALSE))
           )
         )
}

# create data frame for indices to be recorded
n <- length(hodsubsamps0820_000000)
num <- rep (NA, n)
res <- data.frame(Hf=num, AEI=num, ACI=num, NDSI=num)

#use function on each list component
for (i in 1:n) res[i,] <- indices(hodsubsamps0820_000000[i])

With this error code:

Error in readWave(x) : 'filename' must be of type character.