str
Basics
str stands for structure, and is a function that allows you to look at the inner workings of your desired variable.
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Examples
How do I get the number of rows and columns in the mtcars dataset?
Click to see solution
mtcars is a dataset built-in to R, so we don’t have to do anything special before analyzing it with str. You can look at all the built-in R datasets by executing data() in the console.
str(mtcars)'data.frame': 32 obs. of 11 variables: $ mpg : num 21 21 22.8 21.4 18.7 18.1 14.3 24.4 22.8 19.2 ... $ cyl : num 6 6 4 6 8 6 8 4 4 6 ... $ disp: num 160 160 108 258 360 ... $ hp : num 110 110 93 110 175 105 245 62 95 123 ... $ drat: num 3.9 3.9 3.85 3.08 3.15 2.76 3.21 3.69 3.92 3.92 ... $ wt : num 2.62 2.88 2.32 3.21 3.44 ... $ qsec: num 16.5 17 18.6 19.4 17 ... $ vs : num 0 0 1 1 0 1 0 1 1 1 ... $ am : num 1 1 1 0 0 0 0 0 0 0 ... $ gear: num 4 4 4 3 3 3 3 4 4 4 ... $ carb: num 4 4 1 1 2 1 4 2 2 4 ...
We can see there are 32 observations (rows) of 11 variables (columns), so we have 32 rows and 11 columns.
What are the column types in Loblolly? How are they measuring tree age?
Click to see solution
str(Loblolly)Classes ‘nfnGroupedData’, ‘nfGroupedData’, ‘groupedData’ and 'data.frame': 84 obs. of 3 variables: $ height: num 4.51 10.89 28.72 41.74 52.7 ... $ age : num 3 5 10 15 20 25 3 5 10 15 ... $ Seed : Ord.factor w/ 14 levels "329"<"327"<"325"<..: 10 10 10 10 10 10 13 13 13 13 ... - attr(*, "formula")=Class 'formula' language height ~ age | Seed .. ..- attr(*, ".Environment")=<environment: R_EmptyEnv> - attr(*, "labels")=List of 2 ..$ x: chr "Age of tree" ..$ y: chr "Height of tree" - attr(*, "units")=List of 2 ..$ x: chr "(yr)" ..$ y: chr "(ft)"
Loblolly contains all numbers, and while we have two numeric variables in height and age, Seed is an ordered factor, indicating that the numbers in Seed function as labels.
As for age, our "labels" section shows us $ x refers to the age of the tree, and going to the corresponding row in "units" tells us that age is measured in years.
Just by glancing at the data and the str output, we see that the experiment involved height measurements on 14 different seed types after 3, 5, 10, 15, 20, and 25 years.