The Power of dplyr in R - part 2

Let's continue our adventure with dplyr package. In the previous article I introduced select() function which select a subset of columns. Today we will focus on how to pick the observation and add a new column. We will continue using mtcars dataset which is included in your R base program.

Also I would like to say that all the posts I publish here requires basic knowledge of R and R Studio program. If you are totally new in R and don't have it installed on your computer I strongly recommend you to find some on-line tutorials and start with R fundamentals.

library(dplyr)
data("mtcars")
head(mtcars)

Now, let's introduce function:

filter()    filter a subset of rows (pick the observation) 

head(filter(.data=mtcars,mpg>20 & vs==0)) #filter rows where mpg>20 and vs= 0

          mpg cyl  disp  hp drat    wt  qsec vs am gear carb

Mazda RX4      21   6 160.0 110 3.90 2.620 16.46  0  1    4    4

Mazda RX4 Wag  21   6 160.0 110 3.90 2.875 17.02  0  1    4    4

Porsche 914-2  26   4 120.3  91 4.43 2.140 16.70  0  1    5    2

filter() with between() function:

filter(.data=mtcars,between(mpg,18,20)) #filter rows where values of mpg are between 18 and 2

                    mpg cyl  disp  hp drat    wt  qsec vs am gear  carb

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

Merc 280          19.2   6 167.6 123 3.92 3.440 18.30  1  0    4    4

Pontiac Firebird  19.2   8 400.0 175 3.08 3.845 17.05  0  0    3    2

Ferrari Dino      19.7   6 145.0 175 3.62 2.770 15.50  0  1    5    6

slice()  select rows using their position - rows IDs (integer location) 

slice(.data = mtcars, 1:3) #choosing first three rows of the mtcars dataset

               mpg cyl disp  hp drat    wt  qsec vs am gear carb

Mazda RX4     21.0   6  160 110 3.90 2.620 16.46  0  1    4    4

Mazda RX4 Wag 21.0   6  160 110 3.90 2.875 17.02  0  1    4    4

Datsun 710    22.8   4  108  93 3.85 2.320 18.61  1  1    4    1

mutate()  compute a new column (add a new variable while keeping the base variables) 

head(mutate(.data=mtcars,new=mpg/cyl)) #add a new variable while keeping the base variables

  mpg  cyl disp  hp  drat  wt  qsec  vs am  gear carb    new

1 21.0   6  160 110 3.90 2.620 16.46  0  1    4    4 3.500000

2 21.0   6  160 110 3.90 2.875 17.02  0  1    4    4 3.500000

3 22.8   4  108  93 3.85 2.320 18.61  1  1    4    1 5.700000

4 21.4   6  258 110 3.08 3.215 19.44  1  0    3    1 3.566667

5 18.7   8  360 175 3.15 3.440 17.02  0  0    3    2 2.337500

6 18.1   6  225 105 2.76 3.460 20.22  1  0    3    1 3.016667

transmute()  calculates new variables while dropping the base ones. 

head(transmute(.data=mtcars,new=mpg/cyl)) #calculates new variables while dropping the base ones.

new
1 3.500000
2 3.500000
3 5.700000
4 3.566667
5 2.337500
6 3.016667