Helper functions to create common types of constraint matrices,
for use with `Wald_test`

to conduct Wald-type tests of linear
contrasts from a fitted regression model.

## Usage

```
constrain_zero(constraints, coefs, reg_ex = FALSE)
constrain_equal(constraints, coefs, reg_ex = FALSE)
constrain_pairwise(constraints, coefs, reg_ex = FALSE, with_zero = FALSE)
```

## Arguments

- constraints
Set of constraints to test. Can be logical (using

`TRUE`

to specify which coefficients to constrain), integer (specify the index of coefficients to constrain), character (specify the names of the coefficients to constrain), or a regular expression.- coefs
Vector of coefficient estimates, used to determine the column dimension of the constraint matrix. Can be omitted if the function is called inside

`Wald_test()`

.- reg_ex
Logical indicating whether

`constraints`

should be interpreted as a regular expression. Defaults to`FALSE`

.- with_zero
Logical indicating whether coefficients should also be compared to zero. Defaults to

`FALSE`

.

## Details

Constraints can be specified as character vectors, regular
expressions (with `reg_ex = TRUE`

), integer vectors, or logical
vectors.

`constrain_zero()`

Creates a matrix that constrains a specified set of
coefficients to all be equal to zero.

`constrain_equal()`

Creates a matrix that constrains a specified set
of coefficients to all be equal.

`constrain_pairwise()`

Creates a list of constraint matrices
consisting of all pairwise comparisons between a specified set of
coefficients. If `with_zero = TRUE`

, then the list will also include a
set of constraint matrices comparing each coefficient to zero.

## Examples

```
if (requireNamespace("carData", quietly = TRUE)) withAutoprint({
data(Duncan, package = "carData")
Duncan$cluster <- sample(LETTERS[1:8], size = nrow(Duncan), replace = TRUE)
Duncan_fit <- lm(prestige ~ 0 + type + income + type:income + type:education, data=Duncan)
# Note that type:income terms are interactions because main effect of income is included
# but type:education terms are separate slopes for each unique level of type
Duncan_coefs <- coef(Duncan_fit)
# The following are all equivalent
constrain_zero(constraints = c("typeprof:income","typewc:income"),
coefs = Duncan_coefs)
constrain_zero(constraints = ":income", coefs = Duncan_coefs,
reg_ex = TRUE)
constrain_zero(constraints = 5:6, coefs = Duncan_coefs)
constrain_zero(constraints = c(FALSE, FALSE, FALSE, FALSE, TRUE, TRUE, FALSE, FALSE, FALSE),
coefs = Duncan_coefs)
# The following are all equivalent
constrain_equal(c("typebc:education","typeprof:education","typewc:education"),
Duncan_coefs)
constrain_equal(":education", Duncan_coefs, reg_ex = TRUE)
constrain_equal(7:9, Duncan_coefs)
constrain_equal(c(FALSE,FALSE,FALSE,FALSE,FALSE,FALSE,TRUE,TRUE,TRUE),
Duncan_coefs)
# Test pairwise equality of the education slopes
constrain_pairwise(":education", Duncan_coefs,
reg_ex = TRUE)
# Test pairwise equality of the income slopes, plus compare against zero
constrain_pairwise(":income", Duncan_coefs,
reg_ex = TRUE, with_zero = TRUE)
})
#> > data(Duncan, package = "carData")
#> > Duncan$cluster <- sample(LETTERS[1:8], size = nrow(Duncan), replace = TRUE)
#> > Duncan_fit <- lm(prestige ~ 0 + type + income + type:income + type:education,
#> + data = Duncan)
#> > Duncan_coefs <- coef(Duncan_fit)
#> > constrain_zero(constraints = c("typeprof:income", "typewc:income"), coefs = Duncan_coefs)
#> [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9]
#> [1,] 0 0 0 0 1 0 0 0 0
#> [2,] 0 0 0 0 0 1 0 0 0
#> > constrain_zero(constraints = ":income", coefs = Duncan_coefs, reg_ex = TRUE)
#> [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9]
#> [1,] 0 0 0 0 1 0 0 0 0
#> [2,] 0 0 0 0 0 1 0 0 0
#> > constrain_zero(constraints = 5:6, coefs = Duncan_coefs)
#> [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9]
#> [1,] 0 0 0 0 1 0 0 0 0
#> [2,] 0 0 0 0 0 1 0 0 0
#> > constrain_zero(constraints = c(FALSE, FALSE, FALSE, FALSE, TRUE, TRUE,
#> + FALSE, FALSE, FALSE), coefs = Duncan_coefs)
#> [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9]
#> [1,] 0 0 0 0 1 0 0 0 0
#> [2,] 0 0 0 0 0 1 0 0 0
#> > constrain_equal(c("typebc:education", "typeprof:education", "typewc:education"),
#> + Duncan_coefs)
#> [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9]
#> [1,] 0 0 0 0 0 0 -1 1 0
#> [2,] 0 0 0 0 0 0 -1 0 1
#> > constrain_equal(":education", Duncan_coefs, reg_ex = TRUE)
#> [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9]
#> [1,] 0 0 0 0 0 0 -1 1 0
#> [2,] 0 0 0 0 0 0 -1 0 1
#> > constrain_equal(7:9, Duncan_coefs)
#> [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9]
#> [1,] 0 0 0 0 0 0 -1 1 0
#> [2,] 0 0 0 0 0 0 -1 0 1
#> > constrain_equal(c(FALSE, FALSE, FALSE, FALSE, FALSE, FALSE, TRUE, TRUE,
#> + TRUE), Duncan_coefs)
#> [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9]
#> [1,] 0 0 0 0 0 0 -1 1 0
#> [2,] 0 0 0 0 0 0 -1 0 1
#> > constrain_pairwise(":education", Duncan_coefs, reg_ex = TRUE)
#> $`typeprof:education - typebc:education`
#> [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9]
#> [1,] 0 0 0 0 0 0 -1 1 0
#>
#> $`typewc:education - typebc:education`
#> [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9]
#> [1,] 0 0 0 0 0 0 -1 0 1
#>
#> $`typewc:education - typeprof:education`
#> [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9]
#> [1,] 0 0 0 0 0 0 0 -1 1
#>
#> > constrain_pairwise(":income", Duncan_coefs, reg_ex = TRUE, with_zero = TRUE)
#> $`typeprof:income`
#> [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9]
#> [1,] 0 0 0 0 1 0 0 0 0
#>
#> $`typewc:income`
#> [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9]
#> [1,] 0 0 0 0 0 1 0 0 0
#>
#> $`typewc:income - typeprof:income`
#> [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9]
#> [1,] 0 0 0 0 -1 1 0 0 0
#>
```