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R Mean
Mean, Median, and Mode
In statistics, there are often three values that interests us:
- Mean - The average value
- Median - The middle value
- Mode - The most common value
Mean
To calculate the average value (mean) of a variable from the mtcars data set, find the sum of all values, and divide the sum by the number of values.
Sorted observation of wt(weight)
| 1.513 | 1.615 | 1.835 | 1.935 | 2.140 | 2.200 | 2.320 | 2.465 |
| 2.620 | 2.770 | 2.780 | 2.875 | 3.150 | 3.170 | 3.190 | 3.215 |
| 3.435 | 3.440 | 3.440 | 3.440 | 3.460 | 3.520 | 3.570 | 3.570 |
| 3.730 | 3.780 | 3.840 | 3.845 | 4.070 | 5.250 | 5.345 | 5.424 |
Luckily for us, the mean() function in R can do it for you:
Example
Find the average weight (wt) of a car:
mean(Data_Cars$wt)
Result
[1] 3.21725
Median
The median is the average value, after you have set all the values.
If we look at the wt variable values (from the mtcars data set), we will see that there are two numbers in the middle:
Sorted observation of wt(weight)
| 1.513 | 1.615 | 1.835 | 1.935 | 2.140 | 2.200 | 2.320 | 2.465 |
| 2.620 | 2.770 | 2.780 | 2.875 | 3.150 | 3.170 | 3.190 | 3.215 |
| 3.435 | 3.440 | 3.440 | 3.440 | 3.460 | 3.520 | 3.570 | 3.570 |
| 3.730 | 3.780 | 3.840 | 3.845 | 4.070 | 5.250 | 5.345 | 5.424 |
Note: If there are two numbers in the middle, you must divide the sum of those numbers by two, in order to find the media.
Fortunately, R has a function for all of that: Just use the median() function to get the average value:
Example
Find the mid point value of weight(wt):
median(Data_Cars$wt)
Result
[1] 3.325
Mode
Mode value is the value that occurs most of the time.
R has no function to calculate mode. However, we can build our career to get it.
If we look at the wt variable values (from the mtcars data set), we will see that the numbers 3.440 are often displayed:
Sorted observation fo wt(weight)
| 1.513 | 1.615 | 1.835 | 1.935 | 2.140 | 2.200 | 2.320 | 2.465 |
| 2.620 | 2.770 | 2.780 | 2.875 | 3.150 | 3.170 | 3.190 | 3.215 |
| 3.435 | 3.440 | 3.440 | 3.440 | 3.460 | 3.520 | 3.570 | 3.570 |
| 3.730 | 3.780 | 3.840 | 3.845 | 4.070 | 5.250 | 5.345 | 5.424 |
Instead of counting ourselves, we can use the following code to find the mode:
Example
names(sort(-table(Data_Cars$wt)))[1]
Result
[1] "3.44"
From the example above, we now know that the number appearing multiple times in mtcars wt variable is 3.44 or 3.440 lbs.