Test 04 - R matrices

list ( h="P", m="M", c=T ) [[ "c" ]]

• "P"

• "M"

• TRUE

• NULL

list ( h="P", m="M", c=T ) $h

• "P"

• "M"

• TRUE

• NULL

list ( h="P", m="M", c=T) [ c(-2) ]

• $h      

  [1] "P"

• $m      

  [1] "M"

• $h           

  [1] "P"

  $c           

  [1] TRUE

• NULL

matrix ( 1:3 , 2, 3) [ , 1 ]

• [1] 1 3 2

• [1] 1 2

• [1] 2 1 3

• [1] 3 1

matrix(c(1, 1, 1, 4, 2, 3), ncol=2, byrow=T)

•         [ ,1]  [,2]

  [1, ]      1     1

  [2, ]      1     4

  [3, ]      2     3

•         [ ,1]  [,2]

  [1, ]      1     4

  [2, ]      1     2

  [3, ]      1     3

•        [ ,1]  [ ,2] [ ,3]

  [1,]   1      1      1

  [2,]  4     2      3

•        [ ,1]  [ ,2] [ ,3]

  [1,]   1     1      2

  [2,]  1     4      3

matrix(1,2,2) + matrix(2,2,2)

•         [ ,1]  [,2]

  [1, ]      2     2

  [2, ]      2     2

•         [ ,1]  [,2]

  [1, ]      3     3

  [2, ]      3     3

•         [ ,1]  [,2]

  [1, ]      4     4

  [2, ]      4     4

• Error:

matrix(1,2,2) * matrix(2,2,2)

•         [ ,1]  [,2]

  [1, ]      2     2

  [2, ]      2     2

•         [ ,1]  [,2]

  [1, ]      3     3

  [2, ]      3     3

•         [ ,1]  [,2]

  [1, ]      4     4

  [2, ]      4     4

• Error:

apply( matrix( c(1,2), 2,2 ), 2, mean)

• [1] 1 2

• [1] 1 1

• [1] 2 2

• [1] 1.5 1.5

apply( matrix( c(1,2), 2,2, T), 2, mean)

• [1] 1 2

• [1] 1 1

• [1] 2 2

• [1] 1.5 1.5

rowMeans( matrix( c(1,2,3), 3,3 ))

• [1] 1 2 3

• [1] 1 1 1

• [1] 2 2 2

• [1] 1.5 1.5 1.5