Sum object in a column between an interval defined by another dataframe - r

Question

I am trying to obtain the sum of values of a column (B) based on the interval between two values on another column (A) in a "reference" dataframe (df):
A <- seq(1:10)
B <- c(4,3,5,7,5,7,4,7,3,7)
df <- data.frame(A,B)
I have found two ways of doing this:
y <- sum(subset(df, A < 3 & A >= 1, select = "B"))
> y
[1] 7
and
z <- with(df,sum(df[A<3 & A>=1,"B"]))
> z
[1] 7
However, I would like to do this based on a two vectors of values stored on another dataframe
C <- c(3,7,7)
D <- c(1,1,5)
df2 <- data.frame(C,D)
to obtain a column of y values for each pair of C and D values.
I have created a function:
myfn <- function(c,d) {
y <-sum(subset(df, A < c & A >= d, select = "B"))
return(y)
}
Which works fine with numbers
myfn(3,1)
[1] 7
but not with vectors.
myfn(c=C,d=D)
[1] 19
Warning messages:
1: In A < a :
longer object length is not a multiple of shorter object length
2: In A >= b :
longer object length is not a multiple of shorter object length
> myfn(df2$C,df2$D)
[1] 19
Warning messages:
1: In A < a :
longer object length is not a multiple of shorter object length
2: In A >= b :
longer object length is not a multiple of shorter object length
>
Does anyone have any suggestion about how I could calculate such interval for sequence of values?

Answer 1

Try:
mapply(myfn, C, D)
# [1] 7 31 12
The problem is that your function is not naturally vectorized. You can see that because your return value is a sum of the inputs, and sum is not a vectorized operation.
Beyond that, if you look at myfn, the expression A < c & A >= d doesn't make sense when c and d have more than one value. There, you are comparing each value in df to the corresponding value in your C and D vectors (so first value to first, second to second, etc.), instead of comparing all the values in df to each value in C and D in turn.
By using mapply, I'm basically looping through your function with as arguments a single value from C and D at a time.
Fortunately in your case it turns out that C,D have different number of elements than df, so you actually got a warning. If they were the same length you would not have gotten a warning and you would have gotten a single value answer, instead of the three you are presumably looking for.
There are better ways to do this, but the mapply approach is pretty trivial here and works with your code pretty much as is.

Answer 2

Another way...
is.between <- function(x,vec){
return(x>=min(vec) & x<max(vec))
}
apply(df2,1,function(x){sum(df[is.between(df$A,x),]$B)})
# [1] 7 31 12