slicetensor: Working with the indices of a tensor (accessing, slicing,...

In tensorA: Advanced Tensor Arithmetic with Named Indices

Description

Indexing of tensors allows beside the ordinary selection of ranges of indices the renaming of indices. The functions are mainly here to keep the the tensor property of the results.

Usage

slice.tensor(X,i,what,drop=FALSE)
## Methods for class tensor
# X[...,drop=TRUE]
# X[...,drop=TRUE] <- value
# X[[...,drop=TRUE]]
# X[[...,drop=TRUE]] <- value

Arguments

X	A tensor
i	an index given as number or character
what	levels of the index, a number or a character from dimnames
drop	a boolean, if true, indices with only a single level are removed
...	arguments of the form name=indices, and for the [[ ]] functions it also allowed to give names from the corresponding dimnames name=c("a","b") to select indices by names or name=~newname to rename dimensions, the first use makes a usual array access in the given dimension, where [[ ]] only supports a single index, while [ ] allows vectors. The other type changes the names.

Details

The functions allow to rename dimensions and to take select a part of the tensor.

Value

a new tensor with dimensions renamed or individual levels selected

Author(s)

K. Gerald van den Boogaart

See Also

einstein.tensor

Examples

A <- to.tensor(1:20,c(A=2,B=2,C=5))
A[C=1]
A[C=1:3]
A[[B=~b]]                  # renaming dimensions
A[[B=~b,A=~aaa]]      
A[[B=~b,A=~aaa,aaa=1]]      
A[[A=1,B=~gamma]][C=1:2]
A 

Example output

Attaching package: 'tensorA'

The following object is masked from 'package:base':

    norm

[1] 1
attr(,"class")
[1] "tensor"
[1] 1 2 3
attr(,"class")
[1] "tensor"
, , 1

      b
A      [,1] [,2]
  [1,]    1    3
  [2,]    2    4

, , 2

      b
A      [,1] [,2]
  [1,]    5    7
  [2,]    6    8

, , 3

      b
A      [,1] [,2]
  [1,]    9   11
  [2,]   10   12

, , 4

      b
A      [,1] [,2]
  [1,]   13   15
  [2,]   14   16

, , 5

      b
A      [,1] [,2]
  [1,]   17   19
  [2,]   18   20

attr(,"class")
[1] "tensor"
, , 1

      b
aaa    [,1] [,2]
  [1,]    1    3
  [2,]    2    4

, , 2

      b
aaa    [,1] [,2]
  [1,]    5    7
  [2,]    6    8

, , 3

      b
aaa    [,1] [,2]
  [1,]    9   11
  [2,]   10   12

, , 4

      b
aaa    [,1] [,2]
  [1,]   13   15
  [2,]   14   16

, , 5

      b
aaa    [,1] [,2]
  [1,]   17   19
  [2,]   18   20

attr(,"class")
[1] "tensor"
      C
b      [,1] [,2] [,3] [,4] [,5]
  [1,]    1    5    9   13   17
  [2,]    3    7   11   15   19
attr(,"class")
[1] "tensor"
[1] 1 3
attr(,"class")
[1] "tensor"
, , 1

      B
A      [,1] [,2]
  [1,]    1    3
  [2,]    2    4

, , 2

      B
A      [,1] [,2]
  [1,]    5    7
  [2,]    6    8

, , 3

      B
A      [,1] [,2]
  [1,]    9   11
  [2,]   10   12

, , 4

      B
A      [,1] [,2]
  [1,]   13   15
  [2,]   14   16

, , 5

      B
A      [,1] [,2]
  [1,]   17   19
  [2,]   18   20

attr(,"class")
[1] "tensor"

tensorA documentation built on Nov. 20, 2020, 9:07 a.m.