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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
Try it Yourself »

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
Try it Yourself »

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"
Try it Yourself »

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