How do I replace empty dataframe/data.tables from a list with a placeholder data.table?

Question

This post How do I remove empty data frames from a list? talks about removing empty dataframes. How do i remove empty dataframes(nrow =0) from a list and replace them with 1 row placeholder dataframes/data.tables?

M1 <- data.frame(matrix(1:4, nrow = 2, ncol = 2))

M2 <- data.frame(matrix(nrow = 0, ncol = 0))

M3 <- data.frame(matrix(9:12, nrow = 2, ncol = 2))

mlist <- list(M1, M2, M3)



placeholder  = data.table(a=1,b=1)

I tried:

lapply(mlist, function(x) ifelse(nrow(fundslist[[x]]) == 0, placeholder, x))

Answer 1

One option would be using lengths

mlist[!lengths(mlist)] <- list(placeholder)
str(mlist)
#List of 3
# $ :'data.frame':       2 obs. of  2 variables:
#  ..$ X1: int [1:2] 1 2
#  ..$ X2: int [1:2] 3 4
# $ :Classes ‘data.table’ and 'data.frame':      1 obs. of  2 variables:
#  ..$ a: num 1
#  ..$ b: num 1
#  ..- attr(*, ".internal.selfref")=<externalptr> 
# $ :'data.frame':       2 obs. of  2 variables:
#  ..$ X1: int [1:2] 9 10
#  ..$ X2: int [1:2] 11 12

How do I replace empty dataframe/data.tables from a list with a placeholder data.table?

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