Extract.clifford {clifford} | R Documentation |

Extract or replace subsets of cliffords.

```
## S3 method for class 'clifford'
C[index, ...]
## S3 replacement method for class 'clifford'
C[index, ...] <- value
coeffs(x)
coeffs(x) <- value
list_modifier(B)
getcoeffs(C, B)
```

`C` , `x` |
A clifford object |

`index` |
elements to extract or replace |

`value` |
replacement value |

`B` |
A list of integer vectors, terms |

`...` |
Further arguments |

Extraction and replacement methods. The extraction method uses
`getcoeffs()`

and the replacement method uses low-level helper
function `c_overwrite()`

.

In the extraction function `a[index]`

, if `index`

is a list,
further arguments are ignored; if not, the dots are used. If
`index`

is a list, its elements are interpreted as integer vectors
indicating which terms to be extracted (even if it is a `disord`

object). If `index`

is a `disord`

object, standard
consistency rules are applied. The extraction methods are designed so
that idiom such as `a[coeffs(a)>3]`

works.

For replacement methods, the standard use-case is `a[i] <- b`

in
which argument `i`

is a list of integer vectors and `b`

a
length-one numeric vector. Otherwise, to manipulate parts of a clifford
object, use `coeffs(a) <- value`

; this effectively leverages
`disord`

formalism. Idiom such as `a[coeffs(a)<2] <- 0`

is
not currently implemented (to do this, use ```
coeffs(a)[coeffs(a)<2]
<- 0
```

). Replacement using a list-valued index, as in ```
A[i] <-
value
```

uses an ugly hack if `value`

is zero. Replacement methods
are not yet finalised and not yet fully integrated with the
`disordR`

package.

Idiom such as `a[] <- b`

follows the `spray`

package. If
`b`

is a length-one scalar, then `coeffs(a) <- b`

has the same
effect as `a[] <- b`

.

Functions `terms()`

[see `term.Rd`

] and `coeffs()`

extract the terms and coefficients from a clifford object. These
functions return `disord`

objects but the ordering is consistent
between them (an extended discussion of this phenomenon is presented in
the `mvp`

package).

Function `coeffs<-()`

(idiom `coeffs(a) <- b`

) sets all
coefficients of `a`

to `b`

. This has the same effect as
`a[] <- b`

.

Extraction and replacement methods treat `0`

specially, translating
it (via `list_modifier()`

) to `numeric(0)`

.

Extracting or replacing a list with a repeated elements is usually a Bad
Idea (tm). However, if option `warn_on_repeats`

is set to
`FALSE`

, no warning will be given (and the coefficient will be the
sum of the coefficients of the term; see the examples).

Function `getcoeffs()`

is a lower-level helper function that lacks
the succour offered by `[.clifford()`

. It returns a numeric vector
[not a `disord`

object: the order of the elements is determined by
the order of argument `B`

]. Compare standard extraction, eg
`a[index]`

, which returns a clifford object.

```
A <- clifford(list(1,1:2,1:3),1:3)
B <- clifford(list(1:2,1:6),c(44,45))
A[1,c(1,3,4)]
A[2:3, 4] <- 99
A[] <- B
# clifford(list(1,1:2,1:2),1:3) # would give a warning
options("warn_on_repeats" = FALSE)
clifford(list(1,1:2,1:2),1:3) # works; 1e1 + 5e_12
options("warn_on_repeats" = TRUE) # return to default behaviour.
```

[Package *clifford* version 1.0-8 Index]