R - readRDS() & load() fail to give identical data.tables as the original

Question

Background

I tried to replace some CSV output files with rds files to improve efficiency. These are intermediate files that wi

Answer 1

I happen to find a way that resolves the issue (disclaimer: it's a rather inelegant way but it works!) - adding then deleting a dummy column in the loaded data table leads to identical being 'True'. I have also successfully replaced csv with rds intermediate files in my own code.

To be honest, I don't understand enough of the inner workings of R nor data table to know why it works, so any explanations and/or more elegant solutions would be welcomed.

library( data.table )

aDT <- data.table( a=1:10, b=LETTERS[1:10] )
saveRDS( aDT, file = "aDT.rds")
bDT <- readRDS( file = "aDT.rds" )
identical( aDT, bDT, ignore.environment = T )  # Gives 'False'

bDT[ , aaa := NA ]; bDT[ , aaa := NULL ]
identical( aDT, bDT, ignore.environment = T )  # Now gives 'True'


# Using the add-del-col 'trick' works here too
aDT2 <- data.table( a=1:10, b=LETTERS[1:10] )
save( aDT2, file = "aDT2.RData")
bDT2 <- aDT2; rm( aDT2 )
load( file = "aDT2.RData" )
identical( aDT2, bDT2, ignore.environment = T )  # Gives 'False'

aDT2[ , aaa := NA ]; aDT2[ , aaa := NULL ]
identical( aDT2, bDT2, ignore.environment = T )  # Now gives 'True'