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R comes with three types to store lists of homogenous objects: vector, matrix and array.
As far as I can tell:
vector is special cases for 1 dimension arraysmatrix is a special case for 2 dimensions arraysarray can also have any dimension level (including 1 and 2).What is the difference between using 1D arrays over vectors and 2D arrays over matrices? Do we need to cast between those, or will it happen automagically?
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4. A vector is an array of numbers with a single index while a matrix is an array of numbers with two indices. 5. While a vector is used to represent magnitude and direction, a matrix is used to represent linear transformations and keep track of coefficients in linear equations.
A matrix is a two-dimensional (r × c) object (think a bunch of stacked or side-by-side vectors). An array is a three-dimensional (r × c × h) object (think a bunch of stacked r × c matrices). All elements in an array must be of the same data type (character > numeric > logical).
A vector is a list of numbers (can be in a row or column), A matrix is an array of numbers (one or more rows, one or more columns).
Answer: We usually reserve the word "vector" to denote an array that consists of only one column , i.e. is m-by-1, or only one row, i.e is 1-by-n. An array in MATLAB is a generic word that can mean a vector, a matrix, or a higher dimensional object, such as a "matrix" with three or more indices.
There is no difference between a matrix and a 2D array:
> x <- matrix(1:10, 2) > y <- array(1:10, c(2, 5)) > identical(x, y) [1] TRUE ... matrix is just a more convenient constructor, and there are many functions and methods that only accept 2D arrays (a.k.a. matrices).
Internally, arrays are just vectors with a dimension attribute:
... > attributes(x) $dim [1] 2 5 > dim(x) <- NULL > x [1] 1 2 3 4 5 6 7 8 9 10 > z <- 1:10 > dim(z) <- c(2, 5) > is.matrix(z) [1] TRUE To cite the language definition:
Matrices and arrays are simply vectors with the attribute
dimand optionallydimnamesattached to the vector.[...]
The
dimattribute is used to implement arrays. The content of the array is stored in a vector in column-major order and thedimattribute is a vector of integers specifying the respective extents of the array. R ensures that the length of the vector is the product of the lengths of the dimensions. The length of one or more dimensions may be zero.A vector is not the same as a one-dimensional array since the latter has a dim attribute of length one, whereas the former has no dim attribute.
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