Replace typeof with class in episode 4

[davebridges]

In lesson 04-data-structures-part1, under data types the user learns using typeof to determine the structure of data. This can be confusing because the typeof of a factor returns an integer not a factor as one might expect. I suggest modifying this lesson to use class instead which returns a data type of factor. This may be less confusing to the new learner. For example:

>cats <- data.frame(coat = c('calico','black','tabby'))
>class(cats$coat)
[1] "factor"
>typeof(cats$coat)
[1] "integer"

[jcoliver]

@davebridges Thanks for that suggestion. I don't think the lesson ever uses typeof on cats$coat, but learners certainly might try it and be confused when they see a factor is type integer. In the Factor section, there is one call to typeof on a factor, but little actual discussion. Even though the lesson introduces both typeof and class, there doesn't seem to be explicit discussion of the difference between the two. See also the discussion at #294 . Discussion @naupaka @mawds ?

[mawds]

I agree it's confusing.

I wonder whether using stringsAsFactors=FALSE when reading the csv files at the start of the lesson might make it easier to introduce the different types of data? This way we are trying to add a number and a string on cats$weight + cats$coat, and when using feline-data_v2.csv with the broken weight column.

typeof() would then always return something intuitive until we get to the factors section, where the reason why typeof(AFACTOR) is integer can be properly explained.

It would mean introducing stringsAsFactors = FALSE without being able to explain it properly though.

[naupaka]

Yes, agreed, factors are a little weird. However, my inclination is to leave the lesson as it is. It is true that if people go poking around on their own, they may get confused, but the pace of a workshop is usually rapid enough that there's not too much of that going on. Also, the fact that typeof(my_factor) returns integer is explicitly addressed later on in the lesson when factors are introduced.

[raynamharris]

To bring this issue back up, I'm inclined to agree with @davebridges.

This section where typeof() is explored is quite long code-wise. There are 5 examples using typeof() but then the types of aren't explained in detail. (I had to google double.)

typeof(3.14)
typeof(1L) # The L suffix forces the number to be an integer, since by default R uses float numbers
typeof(1+1i)
typeof(TRUE)
typeof('banana')

I feel like the question "why doesn't cats$weight + cats$coat work" could be best answered with an example the provide further exploration of the data frame they created

class(cats$coat)
class(cats$weight)

[ahadjixenofontos]

I agree with naupaka that this a learning opportunity. Factors are so central to R that understanding them thoroughly would be beneficial. When typeof(cats$coat) returns "integer" that's a first brush with factor innards, which will be further reinforced later where factors are discussed in more detail.

[jcoliver]

http://swcarpentry.github.io/r-novice-gapminder/guide/