R Max and Min
Max Min
In the previous chapter, we introduced the mtcars data set. We will continue to use this data set throughout the next pages.
You learned from the R Math chapter that R has several built-in math functions. For example, the min() and max() functions can be used to find the lowest or highest
value in a set:
Example
Find the largest and smallest value of the variable hp (horsepower).
Data_Cars <- mtcars
max(Data_Cars$hp)
min(Data_Cars$hp)
Result:
[1] 335
[1] 52
Now we know that the largest horsepower value in the set is 335, and the lowest 52.
We could take a look at the data set and try to find out which car these two values belongs to:
Observation of cars
mpg cyl disp hp drat wt qsec vs am gear carb
Mazda RX4 21.0 6 160.0 110 3.90 2.620 16.46 0 1 4 4
Mazda RX4 Wag 21.0 6 160.0 110 3.90 2.875 17.02 0 1 4 4
Datsun 710 22.8 4 108.0 93 3.85 2.320 18.61 1 1 4 1
Hornet 4 Drive 21.4 6 258.0 110 3.08 3.215 19.44 1 0 3 1
Hornet Sportabout 18.7 8 360.0 175 3.15 3.440 17.02 0 0 3 2
Valiant 18.1 6 225.0 105 2.76 3.460 20.22 1 0 3 1
Duster 360 14.3 8 360.0 245 3.21 3.570 15.84 0 0 3 4
Merc 240D 24.4 4 146.7 62 3.69 3.190 20.00 1 0 4 2
Merc 230 22.8 4 140.8 95 3.92 3.150 22.90 1 0 4 2
Merc 280 19.2 6 167.6 123 3.92 3.440 18.30 1 0 4 4
Merc 280C 17.8 6 167.6 123 3.92 3.440 18.90 1 0 4 4
Merc 450SE 16.4 8 275.8 180 3.07 4.070 17.40 0 0 3 3
Merc 450SL 17.3 8 275.8 180 3.07 3.730 17.60 0 0 3 3
Merc 450SLC 15.2 8 275.8 180 3.07 3.780 18.00 0 0 3 3
Cadillac Fleetwood 10.4 8 472.0 205 2.93 5.250 17.98 0 0 3 4
Lincoln Continental 10.4 8 460.0 215 3.00 5.424 17.82 0 0 3 4
Chrysler Imperial 14.7 8 440.0 230 3.23 5.345 17.42 0 0 3 4
Fiat 128 32.4 4 78.7 66 4.08 2.200 19.47 1 1 4 1
Honda Civic 30.4 4 75.7 52 4.93 1.615 18.52 1 1 4 2
Toyota Corolla 33.9 4 71.1 65 4.22 1.835 19.90 1 1 4 1
Toyota Corona 21.5 4 120.1 97 3.70 2.465 20.01 1 0 3 1
Dodge Challenger 15.5 8 318.0 150 2.76 3.520 16.87 0 0 3 2
AMC Javelin 15.2 8 304.0 150 3.15 3.435 17.30 0 0 3 2
Camaro Z28 13.3 8 350.0 245 3.73 3.840 15.41 0 0 3 4
Pontiac Firebird 19.2 8 400.0 175 3.08 3.845 17.05 0 0 3 2
Fiat X1-9 27.3 4 79.0 66 4.08 1.935 18.90 1 1 4 1
Porsche 914-2 26.0 4 120.3 91 4.43 2.140 16.70 0 1 5 2
Lotus Europa 30.4 4 95.1 113 3.77 1.513 16.90 1 1 5 2
Ford Pantera L 15.8 8 351.0 264 4.22 3.170 14.50 0 1 5 4
Ferrari Dino 19.7 6 145.0 175 3.62 2.770 15.50 0 1 5 6
Maserati Bora 15.0 8 301.0 335 3.54 3.570 14.60 0 1 5 8
Volvo 142E 21.4 4 121.0 109 4.11 2.780 18.60 1 1 4 2
By observing the table, it looks like the largest hp value belongs to a Maserati Bora, and the lowest belongs to a Honda Civic.
However, it is much easier (and safer) to let R find out this for us.
For example, we can use the which.max() and which.min() functions to find the index position of the max and min value in the table:
Example
Data_Cars <- mtcars
which.max(Data_Cars$hp)
which.min(Data_Cars$hp)
Result:
[1] 31
[1] 19
Or even better, combine which.max() and which.min() with the rownames() function to get the name of the car with the largest and smallest horsepower:
Example
Data_Cars <- mtcars
rownames(Data_Cars)[which.max(Data_Cars$hp)]
rownames(Data_Cars)[which.min(Data_Cars$hp)]
Result:
[1] "Maserati Bora"
[1] "Honda Civic"
Now we know for sure:
Maserati Bora is the car with the highest horsepower, and
Honda Civic is the car with the lowest horsepower.
Outliers
Max and min can also be used to detect outliers. An outlier is a data point that differs from rest of the observations.
Example of data points that could have been outliers in the mtcars data set:
- If maximum of forward gears of a car was 11
- If minimum of horsepower of a car was 0
- If maximum weight of a car was 50 000 lbs
