I'm learning R right now, and realised when I append to a factor it becomes a character. Even when I don't specify factor level this happens. When I look at the order of the numbers, I see that they correspond to the "factor levels" e.g., small is 1. But, I'm wondering why this happens when using this method of appending to vectors.
size_order <- factor(c("small", "medium", "large", "medium", "small", "small"), levels = c("small", "medium", "large"))
size order
> [1] small medium large medium small small
> Levels: small medium large huge
typeof(size_order)
> integer
But then when I append to it, it becomes a character:
size_order <- append(size_order, "small")
size order
> "1" "2" "3" "2" "1" "1" "small"
typeof(size_order)
> [1] "character"
The documentation for ?c states that:
Combine Values into a Vector or List Description This is a generic function which combines its arguments.
The default method combines its arguments to form a vector. All arguments are coerced to a common type which is the type of the returned value, and all attributes except names are removed.
Notice that the all the attributes are stripped off. You are concatenating a factor and a character. A factor is internally stored as an integer. This will be coerced to a character in order to combine the two.
To get the results you want, consider coercing the second string to factor before concatenation. ie
size_order <- factor(c("small", "medium", "large", "medium", "small", "small"), levels = c("small", "medium", "large"))
size_order <- c(size_order, factor('small'))
Which is the same as:
append(size_order, factor('small'))
[1] small medium large medium small small small
Levels: small medium large