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Exercise

Interlude (3)

What if you want all variables but only for the first 10 respondents? Yes, you could use cdc[1:10, 1:9], but that would mean you have to count the number of variables in our set. Fortunately, R makes it easy: if you want all rows or columns, you just leave it empty. So the former can be rewritten as cdc[1:10, ].

By leaving out an index or a range (as you didn't type anything between the comma and the square bracket), you get all the columns. When starting out in R, this is a bit counterintuitive. Similarly, if you leave out an index or range for the rows, you get all the observations. Typing cdc[, 6] will give you all the weights for all 20,000 respondents.

So yes, typing cdc[,] will simply give you the entire data frame cdc.

Instructions

100 XP
  • Assign all variables for the 205th respondent to resp205.
  • Assign the variables height and weight for all respondents to ht_wt.