r data structures

# R’s base data structures can be organised by their dimensionality 
# (1D, 2D, or ND) and whether they’re homogeneous (all contents must be 
# of the same type) or heterogeneous (the contents can be of different 
# types). This gives rise to the five data types most often used in data 
# analysis:

Dimension	Homogeneous		Heterogeneous
1D			Atomic vector	List
2D			Matrix			Data frame
ND			Array

# Note, atomic vectors are always flat (i.e. they can't be nested), they 
#	are usually of type logical, integer, double (often called 
#	numeric), or character, and other R objects are built on atomic 
#	vectors.
# Note, because atomic vectors cannot contain mixed types, if you 
#	combine types, they will be coerced to the most flexible type of 
#	the types you used. In order of increasing flexibility, the types
#	are: logical -> integer -> double -> character