5.2.2 Data Frames vol. 2 | source: http://www.r-exercises.com/2016/11/28/data-frame-exercises-vol-2/

5.2 Data Frames | source: http://www.r-exercises.com/2016/01/04/data-frame-exercises/

5.1.2 Lists vol. 2 | source: http://www.r-exercises.com/2016/12/27/list-exercises-vol-2/

5.1 Lists | source: http://www.r-exercises.com/2015/12/31/list-exercises/

4.4 Matrix Operations | source: http://www.r-exercises.com/2016/08/22/matrix-operations/

4.3 Binding | source: http://www.r-exercises.com/2016/02/22/bind-exercises/

4.2 Arrays | source: http://www.r-exercises.com/2015/12/01/array-exercises/

4.1.2 Matrices Vol. 2 | source: http://www.r-exercises.com/2016/12/08/matrix-vol-2-exercises/

4.1 Matrices | source: http://www.r-exercises.com/2015/11/28/matrix-exercises/

3.1 Factors | source: http://www.r-exercises.com/2015/12/28/factor-exercises/

2.2 Practical uses of R object modes: some examples | source: http://www.r-exercises.com/2016/02/16/practical-uses-of-r-object-modes-some-examples/

2.1 Modes | source: http://www.r-exercises.com/2016/02/14/mode-exercises/

1.6 Index Vectors | source: http://www.r-exercises.com/2015/12/21/index-vectors/

1.4 Missing Values | http://www.r-exercises.com/2015/12/14/missing-values/

1.3 Logical vectors and operators | source: http://www.r-exercises.com/2015/11/25/logical-vectors-and-operators/

1.2.2 Regular Sequences Exercises vol. 2 source: http://www.r-exercises.com/2016/11/09/regular-sequences-2/

1.2 Regular Sequences | source: http://www.r-exercises.com/2015/10/23/regular-sequences/

1.5 Character Vectors | source: http://r-exercises.com/2015/12/18/character-vector-exercises/

1.2 Vectors vol. 2 | source: http://r-exercises.com/2016/11/15/vector-exercises-vol-2/

1.1 Vectors | source: http://r-exercises.com/2015/10/09/vector-exercises/