Equality comparison in an if statement in R - r

Question

I have a list of data.frames:
book=list(ask,bid)
and I want to iterate through each data.frame like so:
book.total_volumes <- function(book) {
bid_total_volume=0
ask_total_volume=0
for(book in book) {
if(book=="bid"){
for(value in book[,"volumes"]) {
bid_total_volume=bid_total_volume+value }
}
if(book=="ask"){
for(value in book[,"volumes"]) {
ask_total_volume=ask_total_volume+value }
}
}
print(bid_total_volume)
print(ask_total_volume)
}
book.total_volumes(book)
when doing the if statement, how can I check if the current book name is equals to "bid" or if it is equals to "ask

Answer 1

The issue here is that the elements of you list book aren't named. Another issue is that I don't think you can define book in book in a loop, this will overwrite the first book variable...
Here is the quick answer using lapply function. It apply the same function to all elements of a list and return the values in the same order.
ask = data.frame(title = c("hello", "book"),
volumes = c(1, 42))
bid = data.frame(title = c("hello", "book"),
volumes = c(12, 1))
book=list(ask,bid)
print(unlist(lapply(book, function(x) sum(x[,"volumes"]))))
A longer version of this could be below. Note that list in R are also ordered.
book.total_volumes <- function(book) {
res <- c(ask = 0, bid = 0)
for(i in 1:length(book)){
res[i] = sum(book[[i]][, "volumes"])
# You can replace sum with a loop but it's good practice in R to vectorise code.
}
print(res)
}
book.total_volumes(book)
If you name the elements of you list, this code will work but this is not very optimal as functions exist to do this in less code.
book=list(ask = ask, bid = bid)
book.total_volumes <- function(book) {
bid_total_volume=0
ask_total_volume=0
for(i in seq_along(book)) {
if(names(book)[i] == "bid"){
for(value in book[[i]][,"volumes"]) {
bid_total_volume = bid_total_volume + value
}
}
if(names(book)[i]=="ask"){
for(value in book[[i]][,"volumes"]) {
ask_total_volume =ask_total_volume + value
}
}
}
print(bid_total_volume)
print(ask_total_volume)
}
book.total_volumes(book)