Merging Embedded Lists with Different Date Formats in R - r

Question

I need to merge two lists with each other but I am not getting what I want and I think it is because the "Date" column is in two different formats. I have a list called li and in this list there are 12 lists each with the following format:
> tail(li$fxe)
Date fxe
3351 2020-06-22 0.0058722768
3352 2020-06-23 0.0044256216
3353 2020-06-24 -0.0044998220
3354 2020-06-25 -0.0027309539
3355 2020-06-26 0.0002832672
3356 2020-06-29 0.0007552346
I am trying to merge each of these unique lists with a different list called factors which looks like :
> tail(factors)
Date Mkt-RF SMB HML RF
3351 20200622 0.0071 0.83 -1.42 0.000
3352 20200623 0.0042 0.15 -0.56 0.000
3353 20200624 -0.0261 -0.52 -1.28 0.000
3354 20200625 0.0112 0.25 0.50 0.000
3355 20200626 -0.0243 0.16 -1.37 0.000
3356 20200629 0.0151 1.25 1.80 0.000
The reason I need this structure is because I am trying to send them to a function I wrote to do linear regressions. But the first line of my function aims to merge these lists. When I merge them I end up with a null structure even thought my lists clearly have the same number of rows. In my function df is li. The embedded list of li is confusing me. Can someone help please?
Function I want to use:
Bf <- function(df, fac){
#This function calculates the beta of the french fama factor #using linear regression
#Input: df = a dataframe containg returns of the security
# fac = dataframe containing excess market retrun and
# french fama 3 factor
#Output: a Beta vectors of the french fama model
temp <- merge(df, fac, by="Date")
temp <- temp[, !names(temp) %in% "Date"]
temp[ ,1] <- temp[,1] - temp$RF return(lm(temp[,1]~temp[,2]+temp[,3]+temp[,4])$coeff)
}

Answer 1

a: you are dealing with data frames and not lists
b: if you want to merge them, you need to modify the factors$date column to match that of li$fxe$date
try to do:
factors$date <- as.Date(strptime(factors$date, format = "%Y%M%d"))
This should convert, the factors column to "Date" format.