Question: I have 4 data frames saved as .csv files or .txt (df1.csv,df2.csv,df3.txt,df4.txt).
I would like to sum all the rows of df1 with df3 and df4 and of df2 with df3 and df4 in a loop. I would like to store the results in two separate sublists (one for df1 and one for df2) of a main list.

Example:

```
df1      df3
colA    colA
5        1
1        4
3        1

df2     df4
colA    colA
0        0
2        0
1        9

```

Output:

I would like to have a list\_ALL which contains listDF1 with the results of the sum of df1 with df3 and df4 and a listDF2 which contains results of df2 with df3 and df4

```
LISTDF1

 df5   df6

 colA   colA
  6      5
  5      1
  4      12

LISTDF2

  df7   df8

  colA  colA
   1    0
   6    2
   2    10

list_ALL<-list()

files.csv<-list.files(pattern = "*.csv")
files.txt<-list.files(pattern = "*.txt")
for (i in 1:length(files.csv)) {
  list_ALL[[i]]<-list()
}
names(listALL)<-files.csv

for (i in 1:length(files.csv))
  for (j in 1:length(files.txt))
    {{ list_ALL[[i]][[j]] <- rowSums([[i]][[j]])}}

```

I tried this however, only the first one of the sublist gets filled up.

Answer: 
Something like this?

```
lst1 <- list(df1<-c(5,1,3), df2<-c(0,2,1))

lst2 <- list(df3<-c(1,4,1), df4<-c(0,0,9))

res_lst <- list()
for(i in seq_along(lst1)){
  for(j in seq_along(lst2)){
       res <- lst1[[i]]+lst2[[j]]
       res_lst <- append(res_lst, list(res))
  }
}

splt_lst <- split(x = res_lst, f = rep(1:2, each=2))

$`1`
$`1`[[1]]
[1] 6 5 4

$`1`[[2]]
[1]  5  1 12

$`2`
$`2`[[1]]
[1] 1 6 2

$`2`[[2]]
[1]  0  2 10

```
```
for (j in 1:length(files))
  {
    cog_out_dat[[j]]<- lapply(meta_exp_dat,function(df) try(read_outcome_data(
      snps = df$SNP,
      filename = files[[j]],
      gene_col = "anno",
      sep = " ",
      chr_col = "CHR",
      pos_col = "BP",
      snp_col = "SNP",
      beta_col = "BETA",
      se_col = "SE",
      effect_allele_col = "ALLELE1",
      other_allele_col = "ALLELE0",
      eaf_col = "EAF",
      pval_col = "P",
      phenotype_col = "DATA"
    )))
  }

```