Because your question is phrased regarding your error message and not whatever your function is trying to accomplish, I will address the error.
- is the ‘binary operator’ your error is referencing, and either
MA (or both) are non-numeric.
A binary operation is a calculation that takes two values (operands) and produces another value (see wikipedia for more).
+ is one such operator: “1 + 1” takes two operands (1 and 1) and produces another value (2). Note that the produced value isn’t necessarily different from the operands (e.g., 1 + 0 = 1).
R only knows how to apply
+ (and other binary operators, such as
-) to numeric arguments:
> 1 + 1  2 > 1 + 'one' Error in 1 + "one" : non-numeric argument to binary operator
When you see that error message, it means that you are (or the function you’re calling is) trying to perform a binary operation with something that isn’t a number.
Your error lies in the use of
[ instead of
Day is a list, subsetting with
[ will return a list, not a numeric vector.
[[, however, returns an object of the class of the item contained in the list:
> Day <- Transaction(1, 2)["b"] > class(Day)  "list" > Day + 1 Error in Day + 1 : non-numeric argument to binary operator > Day2 <- Transaction(1, 2)[["b"]] > class(Day2)  "numeric" > Day2 + 1  3
Transaction, as you’ve defined it, returns a list of two vectors. Above,
Day is a list contain one vector.
Day2, however, is simply a vector.