VGAM (version 1.1-14)

Select: Select Variables for a Formula Response or the RHS of a Formula

Description

Select variables from a data frame whose names begin with a certain character string.

Usage

Select(data = list(), prefix = "y",
       lhs = NULL, rhs = NULL, rhs2 = NULL, rhs3 = NULL,
       as.character = FALSE, as.formula.arg = FALSE, tilde = TRUE,
       exclude = NULL, sort.arg = TRUE)

Value

If as.character = FALSE and

as.formula.arg = FALSE then a matrix such as cbind(y1, y2, y3). If as.character = TRUE and

as.formula.arg = FALSE then a character string such as "cbind(y1, y2, y3)".

If as.character = FALSE and

as.formula.arg = TRUE then a formula such as lhs ~ y1 + y2 + y3. If as.character = TRUE and

as.formula.arg = TRUE then a character string such as "lhs ~ y1 + y2 + y3". See the examples below. By default, if no variables beginning the the value of prefix

is found then a NULL is returned. Setting prefix = " " is a way of selecting no variables.

Details

This is meant as a utility function to avoid manually: (i) making a cbind call to construct a big matrix response, and (ii) constructing a formula involving a lot of terms. The savings can be made because the variables of interest begin with some prefix, e.g., with the character "y".

See Also

vglm, cbind, subset, formula, fill1.

Examples

Pneumo <- pneumo
colnames(Pneumo) <- c("y1", "y2", "y3", "x2")  # The "y" variables are response
Pneumo$x1 <- 1; Pneumo$x3 <- 3; Pneumo$x <- 0; Pneumo$x4 <- 4  # Add these

Select(data = Pneumo)  # Same as with(Pneumo, cbind(y1, y2, y3))
Select(Pneumo, "x")
Select(Pneumo, "x", sort = FALSE, as.char = TRUE)
Select(Pneumo, "x", exclude = "x1")
Select(Pneumo, "x", exclude = "x1", as.char = TRUE)
Select(Pneumo, c("x", "y"))
Select(Pneumo, "z")  # Now returns a NULL
Select(Pneumo, " ")  # Now returns a NULL
Select(Pneumo, prefix = TRUE, as.formula = TRUE)
Select(Pneumo, "x", exclude = c("x3", "x1"), as.formula = TRUE,
       lhs = "cbind(y1, y2, y3)", rhs = "0")
Select(Pneumo, "x", exclude = "x1", as.formula = TRUE, as.char = TRUE,
       lhs = "cbind(y1, y2, y3)", rhs = "0")

# Now a 'real' example:
Huggins89table1 <- transform(Huggins89table1, x3.tij = t01)
tab1 <- subset(Huggins89table1,
               rowSums(Select(Huggins89table1, "y")) > 0)
# Same as
# subset(Huggins89table1, y1 + y2 + y3 + y4 + y5 + y6 + y7 + y8 + y9 + y10 > 0)

# Long way to do it:
fit.th <-
   vglm(cbind(y01, y02, y03, y04, y05, y06, y07, y08, y09, y10) ~ x2 + x3.tij,
        xij = list(x3.tij ~ t01 + t02 + t03 + t04 + t05 + t06 + t07 + t08 +
                            t09 + t10 - 1),
        posbernoulli.t(parallel.t = TRUE ~ x2 + x3.tij),
        data = tab1, trace = TRUE,
        form2 = ~ x2 + x3.tij + t01 + t02 + t03 + t04 + t05 + t06 + t07 + t08 +
                                t09 + t10)
# Short way to do it:
Fit.th <- vglm(Select(tab1, "y") ~ x2 + x3.tij,
               xij = list(Select(tab1, "t", as.formula = TRUE,
                                 sort = FALSE, lhs = "x3.tij", rhs = "0")),
               posbernoulli.t(parallel.t = TRUE ~ x2 + x3.tij),
               data = tab1, trace = TRUE,
               form2 = Select(tab1, prefix = TRUE, as.formula = TRUE))