Subsetting tiny fixes

[carriewright11]

• slide 72 say some old stuff about tb data which we aren't working with anymore - just needs to be deleted
• lab part 3 says 1.3 and 1.4 instead of 3.3, 3.4 etc.

[avahoffman]

In 3.1,

Create a subset called `county_2012` from `county_pop` that only contains the rows for the year 2012 and only the columns: `county_name`,	`state_name`, `population`. `year` should not be included in `county_sub`.

I think this should be county_2012 not county_sub

Re-order the rows of `county_2012` by population in increasing order. Use `arrange()`. What is county with the smallest population?

Missing a word

[carriewright11]

tell them in the slide about errors for filter - remind them how it works- someone got confused - it works on rows based on specified conditions for values across the rows of particular columns

[carriewright11]

Check fhdsl/DaSEH#81 for overlap