PivotalR (version 0.1.18.5)

as.factor-methods: Convert one column of a '>db.obj object into a categorical variable

Description

Convert one column of a db.obj object into a categorical variable. When madlib.lm or madlib.glm are applied onto a db.obj with categorical columns, dummy columns will be created and fitted. The reference level for regressions can be selected using relevel.

Usage

# S4 method for db.obj
as.factor(x)
# S4 method for db.obj
relevel(x, ref, ...)

Arguments

x

A db.obj object. It must have only one column.

ref

A single value, which is the reference level that is used in the regressions.

…

Other arguments passed into the result. Not implemented yet.

Value

A db.Rquery object. It has only one column which is categorical. By default, a reference level is automatically selected in regressions, which is usually the minimum of all levels, but one can easily change the reference level using relevel.

See Also

madlib.lm and madlib.glm can fit categorical variables

When as.db.data.frame creates a table/view, it can create dummy variables for a categorical variable.

Examples

# NOT RUN {
## get help for a method
## help("as.factor,db.obj-method")

<!-- %% @test .port Database port number -->
<!-- %% @test .dbname Database name -->
## set up the database connection
## Assume that .port is port number and .dbname is the database name
cid <- db.connect(port = .port, dbname = .dbname, verbose = FALSE)

## create a temporary table from the example data.frame "abalone"
x <- as.db.data.frame(abalone, conn.id = cid, verbose = FALSE)

## set sex to be a categorical variable
x$sex <- as.factor(x$sex)

fit1 <- madlib.lm(rings ~ . - id, data = x) # linear regression

fit2 <- madlib.glm(rings < 10 ~ . - id, data = x, family = "binomial") # logistic regression

## another temporary table
z <- as.db.data.frame(abalone, conn.id = cid, verbose = FALSE)

## specify factor during fitting
fit3 <- madlib.lm(rings ~ as.factor(sex) + length + diameter, data = z)

## as.factor is automatically used onto text column
## so as.factor is not necessary
fit4 <- madlib.glm(rings < 10 ~ sex + length + diameter, data
= z, family = "binomial")

## using relevel to change the reference level
x$sex <- relevel(x$sex, ref = "M")
madlib.lm(rings ~ . - id, data = x) # use "M" as the reference level

db.disconnect(cid, verbose = FALSE)
# }