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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 on all of the following pages.

You learned in the R Math chapter that R has a few built-in mathematical functions. For example, 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).

Result

We now know that the maximum horse strength in the set is 335, and the lowest is 52.

We can look at the data set and try to determine which of these two numbers belong to the car:

Observation

                     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
    

Looking at the table, it looks like the largest hp number is the Maserati Bora, and the lowest is Honda Civic.

However, it is much easier (and safer) for R to get this for us.

For example, we can use which.max() and which.min() functions to find the index of the largest and smallest value in a table:

Example

Result

Or better yet, combine which.max() and which.min() and rownames() function to get the name of the strongest and smallest car:

Example

Result

Now we know for sure:
The Maserati Bora is a very high-powered car, while the
Honda Civic is a very low-powered car.

Outliers

Max and min can also be used to find outliers. The outlier is a data point that differs from all the noted.

Examples of data points that may be external to 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

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