Matrices and arrays

TODO
Matrices
Arrays
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TODO

link to matrixArithmetic

Matrices

Create a matrix using `matrix()`

age <- c(17, 30, 30, 25, 23, 21)
matrix(age, nrow=3, ncol=2, byrow=FALSE)

     [,1] [,2]
[1,]   17   25
[2,]   30   23
[3,]   30   21

(ageMat <- matrix(age, nrow=2, ncol=3, byrow=TRUE))

     [,1] [,2] [,3]
[1,]   17   30   30
[2,]   25   23   21

Combine rows and columns to a matrix

age    <- c(19, 19, 31, 19, 24)
weight <- c(95, 76, 94, 76, 76)
height <- c(197, 178, 189, 184, 173)
rbind(age, weight, height)

       [,1] [,2] [,3] [,4] [,5]
age      19   19   31   19   24
weight   95   76   94   76   76
height  197  178  189  184  173

cbind(age, weight, height)

     age weight height
[1,]  19     95    197
[2,]  19     76    178
[3,]  31     94    189
[4,]  19     76    184
[5,]  24     76    173

Information about matrices

dim(ageMat)

[1] 2 3

nrow(ageMat)

[1] 2

ncol(ageMat)

[1] 3

prod(dim(ageMat))

[1] 6

Transpose matrices

t(ageMat)

     [,1] [,2]
[1,]   17   25
[2,]   30   23
[3,]   30   21

as.matrix(1:3)

     [,1]
[1,]    1
[2,]    2
[3,]    3

c(ageMat)

[1] 17 25 30 23 30 21

Rows and columns

P       <- 2
Q       <- 3
(pqMat  <- matrix(1:(P*Q), nrow=P, ncol=Q))

     [,1] [,2] [,3]
[1,]    1    3    5
[2,]    2    4    6

(rowMat <- row(pqMat))

     [,1] [,2] [,3]
[1,]    1    1    1
[2,]    2    2    2

(colMat <- col(pqMat))

     [,1] [,2] [,3]
[1,]    1    2    3
[2,]    1    2    3

cbind(rowIdx=c(rowMat), colIdx=c(colMat), val=c(pqMat))

     rowIdx colIdx val
[1,]      1      1   1
[2,]      2      1   2
[3,]      1      2   3
[4,]      2      2   4
[5,]      1      3   5
[6,]      2      3   6

mat <- matrix(sample(1:10, 16, replace=TRUE), 4, 4)
upper.tri(mat)

      [,1]  [,2]  [,3]  [,4]
[1,] FALSE  TRUE  TRUE  TRUE
[2,] FALSE FALSE  TRUE  TRUE
[3,] FALSE FALSE FALSE  TRUE
[4,] FALSE FALSE FALSE FALSE

lower.tri(mat)

      [,1]  [,2]  [,3]  [,4]
[1,] FALSE FALSE FALSE FALSE
[2,]  TRUE FALSE FALSE FALSE
[3,]  TRUE  TRUE FALSE FALSE
[4,]  TRUE  TRUE  TRUE FALSE

Extract and change elements

Row and column indices

ageMat <- matrix(sample(16:35, 6, replace=TRUE), nrow=2, ncol=3)
ageMat[2, 2]

[1] 32

ageMat[2, 2] <- 24
ageMat[2, 2]

[1] 24

ageMat[2,  ]

[1] 19 24 18

ageMat[ , 1]

[1] 26 19

ageMat[ ,  ]

     [,1] [,2] [,3]
[1,]   26   28   26
[2,]   19   24   18

ageMat[ , 1, drop=FALSE]

     [,1]
[1,]   26
[2,]   19

ageMat[ , 2:3]

     [,1] [,2]
[1,]   28   26
[2,]   24   18

ageMat[ , c(1, 3)]

     [,1] [,2]
[1,]   26   26
[2,]   19   18

Index vector

idxVec <- c(1, 3, 4)
ageMat[idxVec]

[1] 26 28 24

Index matrix

ageMatNew   <- ageMat
(replaceMat <- matrix(c(11, 21, 12, 22), nrow=2, ncol=2))

     [,1] [,2]
[1,]   11   12
[2,]   21   22

ageMatNew[ , c(1, 3)] <- replaceMat
ageMatNew

     [,1] [,2] [,3]
[1,]   11   28   12
[2,]   21   24   22

Logical index matrix

(idxMatLog <- ageMat >= 25)

      [,1]  [,2]  [,3]
[1,]  TRUE  TRUE  TRUE
[2,] FALSE FALSE FALSE

ageMat[idxMatLog]

[1] 26 28 26

(idxMatNum <- which(idxMatLog, arr.ind=TRUE))

     row col
[1,]   1   1
[2,]   1   2
[3,]   1   3

ageMat[idxMatNum]

[1] 26 28 26

(idxMat <- arrayInd(idxVec, dim(ageMat)))

     [,1] [,2]
[1,]    1    1
[2,]    1    2
[3,]    2    2

Also see help(Extract)

Sort matrices

age    <- c(19, 19, 31, 19, 24)
weight <- c(95, 76, 94, 76, 76)
height <- c(197, 178, 189, 184, 173)
mat    <- cbind(age, weight, height)
(rowOrder1 <- order(mat[ , "age"]))

[1] 1 2 4 5 3

mat[rowOrder1, ]

     age weight height
[1,]  19     95    197
[2,]  19     76    178
[3,]  19     76    184
[4,]  24     76    173
[5,]  31     94    189

rowOrder2 <- order(mat[ , "age"], partial=mat[ , "weight"])
mat[rowOrder2, ]

     age weight height
[1,]  19     76    178
[2,]  19     76    184
[3,]  19     95    197
[4,]  24     76    173
[5,]  31     94    189

rowOrder3 <- order(mat[ , "weight"], -mat[ , "height"])
mat[rowOrder3, ]

     age weight height
[1,]  19     76    184
[2,]  19     76    178
[3,]  24     76    173
[4,]  31     94    189
[5,]  19     95    197

Arrays

Create arrays

(myArr1 <- array(1:12, c(2, 3, 2),
                 dimnames=list(row=c("f", "m"), column=c("CG", "WL", "T"),
                               layer=c("high", "low"))))

, , layer = high

   column
row CG WL T
  f  1  3 5
  m  2  4 6

, , layer = low

   column
row CG WL  T
  f  7  9 11
  m  8 10 12

Extract and change elements

myArr1[1, 3, 2]

[1] 11

myArr1[2, 1, 2] <- 19
myArr2 <- myArr1*2
myArr2[ , , "high"]

   column
row CG WL  T
  f  2  6 10
  m  4  8 12

Transpose arrays

Switch rows and columns

aperm(myArr1, c(2, 1, 3))

, , layer = high

      row
column f m
    CG 1 2
    WL 3 4
    T  5 6

, , layer = low

      row
column  f  m
    CG  7 19
    WL  9 10
    T  11 12

Switch rows and layers

aperm(myArr1, c(3, 2, 1))

, , row = f

      column
layer  CG WL  T
  high  1  3  5
  low   7  9 11

, , row = m

      column
layer  CG WL  T
  high  2  4  6
  low  19 10 12

Get the article source from GitHub

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Matrices and arrays

TODO

Matrices

Create a matrix using matrix()

Combine rows and columns to a matrix

Information about matrices

Transpose matrices

Rows and columns

Extract and change elements

Sort matrices

Arrays

Create arrays

Extract and change elements

Transpose arrays

Get the article source from GitHub

Create a matrix using `matrix()`