Using apply() and If() statement to sum() two columns - r

Question

I have a dataframe with 2 columns and I want to use a if/else condition when using the apply function to sum() the rows in each column - specifically, for all the rows where Col1 >= Col2 take the sum() of Col1 and store it in variable a, and for all the rows where Col1 < Col2 take the sum() of Col1 and store it in variable b.
For example
df<-data.frame(Col1=c(1,2,3,4,5),Col2=c(5,4,3,2,1))
df
Col1 Col2
1 5
2 4
3 3
4 2
5 1
There are three instances in which Col1 >= Col2, so in Col1 I take the sum() of 3+4+5, which is 12. There are two instances in which Col1 < Col2, so in Col1 I take the sum() of 1+2, which is 3. So
>a
12
>b
3
This is the code I created, but it's still in the works:
apply(df, 1, function(x)
if(df$Col1 >= df$Col2)
a<-sum(df$Col1 >= df$Col2)
else
b<-sum(df$Col1 < df$Col2)
)
The code here doesn't work because it simply adds the number of times the condition is true and not the actual values.

Answer 1

There's really no need for any *apply() functions here, as these are fully vectorized operations. Here's how I might go about it, putting both results into a nice list.
with(df, {
x <- Col1 >= Col2
list(a = sum(Col1[x]), b = sum(Col1[!x]))
})
# $a
# [1] 12
#
# $b
# [1] 3

Answer 2

I'm not sure why you would want to tackle this problem with an using -apply-. It seems like an overkill. Also note that your -apply- statement lacks the margin argument with which you indicate whether you want to apply the function to rows, columns or both (also, the line defining df needs another closing paranthesis).
A simple two line solution would be this:
df<-data.frame(Col1=c(1,2,3,4,5),Col2=c(5,4,3,2,1)
a <- sum(df$Col1[df$Col1 >= df$Col2])
b <- sum(df$Col2[df$Col1 < df$Col2])