Sum a variable across dataframes by an ID variable - r

Question

There are 3 data frames. The ID variable is in the 12th column of each data frame. I created a vector list_cc_q1 that contains all the unique IDs across all data frames (hence each entry in this vector appears in the 12th column of at least one data frame).
I wish to create a vector v1 that adds, for each ID, the values in the 7th column from each data frame which contains that ID (hence v1 would be of the same length as list_cc_q1). Here's the code I'm using:
f1 <- function(x,y){
ifelse(length(get(y)[which(get(y)[x,12]),7])>0, get(y)[which(get(y)[x,12]),7], 0)}
g1 <- function(x){sum(sapply(ls()[1:3], function(y){ f1(x,y)}))}
v1 <- sapply(list_cc_q1, function(z){ g1(z) })
This returns the following error:
Error in get(y)[x, 12] : incorrect number of dimensions
Called from: which(get(y)[x, 12])
I think I've overcomplicated the code, a simpler method will be immensely helpful.
But why doesn't this work?

Answer 1

Not sure I understand correctly, but how about:
library(data.table)
dt <- data.table(value = c(df1[[7]],df2[[7]],df3[[7]]), id = c(df1[[12]],df2[[12]],df3[[12]]))
dt[, .(sum = sum(value)), by = id]
This concatenates the 7th column of each of the three data.frames (df1, df2, df3) to a value column and the 12th column of each of the data.frames (df1, df2, df3) to an id column to form a data.table with two columns (value and id). It then sums the value column by the id column.
EDIT: Your code might not work because of the
ls()[1:3]
The ls() command is executed in the function-environment which does not contain your three data.frames if I see this correctly. You can see this by comparing the following:
ls()[1:3]
# [1] "df1" "df2" "df3"
function_ls <- function(){cat(ls()[1:3])}
function_ls()
# NA NA NA