| mChoice {Hmisc} | R Documentation |
mChoice is a function that is useful for defining a group of
variables on the right side of the formula. The variables can represent
individual choices on a multiple choice question. These choices are
typically factor or character values but may be of any type. Levels
of component factor variables need not be the same; all unique levels
(or unique character values) are collected over all of the multiple
variables. Then a new character vector is formed with integer choice
numbers separated by semicolons. Optimally, a database system would
have exported the semicolon-separated character strings with a
levels attribute containing strings defining value labels
corresponding to the integer choice numbers. mChoice is a
function for creating a multiple-choice variable after the fact.
mChoice variables are explicitly handed by the describe
and summary.formula functions. NAs or blanks in input
variables are ignored.
format.mChoice will convert the multiple choice representation
to text form by substituting levels for integer codes.
as.double.mChoice converts the mChoice object to a
binary numeric matrix, one column per used level (or all levels of
drop=FALSE. This is called by
the user by invoking as.numeric. There is a
print method and a summary method, and a print
method for the summary.mChoice object. The summary
method computes frequencies of all two-way choice combinations, the
frequencies of the top 5 combinations, information about which other
choices are present when each given choice is present, and the
frequency distribution of the number of choices per observation. This
summary output is used in the describe function.
inmChoice creates a logical vector the same length as x
whose elements are TRUE when the observation in x
contains at least one of the codes or value labels in the second argument.
mChoice(..., label='', sort.=TRUE,
sort.levels=c('original','alphabetic'),
add.none=FALSE, drop=TRUE)
## S3 method for class 'mChoice':
format(x, minlength=NULL, sep=";", ...)
## S3 method for class 'mChoice':
as.double(x, drop=FALSE, ...)
## S3 method for class 'mChoice':
print(x, long=FALSE, ...)
## S3 method for class 'mChoice':
summary(object, ncombos=5, minlength=NULL, drop=TRUE, ...)
## S3 method for class 'summary.mChoice':
print(x, prlabel=TRUE, ...)
## S3 method for class 'mChoice':
x[..., drop=FALSE]
inmChoice(x, values)
... |
a series of vectors |
sort. |
By default, choice codes are sorted in ascending numeric
order. Set sort=FALSE to preserve the original left to right
ordering from the input variables. |
label |
a character string label attribute to attach to the matrix created
by mChoice
|
sort.levels |
set sort.levels="alphabetic" to sort the columns of the matrix
created by mChoice alphabetically by category rather than by the
original order of levels in component factor variables (if there were
any input variables that were factors)
|
add.none |
Set add.none to TRUE to make a new category
'none' if it doesn't already exist and if there is an
observations with no choices selected.
|
drop |
set drop=FALSE to keep unused factor levels as columns of the matrix
produced by mChoice
|
x |
an object of class "mchoice" such as that created by
mChoice |
object |
an object of class "mchoice" such as that created by
mChoice |
ncombos |
maximum number of combos. |
minlength |
By default no abbreviation of levels is done in
format and summary. Specify a positive integer to use
abbreviation in those functions. See abbreviate. |
sep |
character to use to separate levels when formatting |
long |
Set to TRUE to print the formatted levels. Otherwise integer
codes are printed.
|
prlabel |
set to FALSE to keep
print.summary.mChoice from printing the variable label and
number of unique values |
values |
a scalar or vector. If values is integer, it is
the choice codes, and if it is a character vector, it is assumed to
be value labels. |
mChoice returns a character vector of class "mChoice"
plus attributes "levels" and "label".
summary.mChoice returns an object of class
"summary.mChoice". inmChoice returns a logical vector.
format.mChoice returns a character vector, and
as.double.mChoice returns a binary numeric matrix.
Frank Harrell
Department of Biostatistics
Vanderbilt University
f.harrell@vanderbilt.edu
options(digits=3)
set.seed(3)
n <- 20
sex <- factor(sample(c("m","f"), n, rep=TRUE))
age <- rnorm(n, 50, 5)
treatment <- factor(sample(c("Drug","Placebo"), n, rep=TRUE))
# Generate a 3-choice variable; each of 3 variables has 5 possible levels
symp <- c('Headache','Stomach Ache','Hangnail',
'Muscle Ache','Depressed')
symptom1 <- sample(symp, n, TRUE)
symptom2 <- sample(symp, n, TRUE)
symptom3 <- sample(symp, n, TRUE)
cbind(symptom1, symptom2, symptom3)[1:5,]
Symptoms <- mChoice(symptom1, symptom2, symptom3, label='Primary Symptoms')
Symptoms
print(Symptoms, long=TRUE)
format(Symptoms[1:5])
inmChoice(Symptoms,'Headache')
levels(Symptoms)
inmChoice(Symptoms, 3)
inmChoice(Symptoms, c('Headache','Hangnail'))
# Note: In this example, some subjects have the same symptom checked
# multiple times; in practice these redundant selections would be NAs
# mChoice will ignore these redundant selections
meanage <- N <- numeric(5)
for(j in 1:5) {
meanage[j] <- mean(age[inmChoice(Symptoms,j)])
N[j] <- sum(inmChoice(Symptoms,j))
}
names(meanage) <- names(N) <- levels(Symptoms)
meanage
N
# Manually compute mean age for 2 symptoms
mean(age[symptom1=='Headache' | symptom2=='Headache' | symptom3=='Headache'])
mean(age[symptom1=='Hangnail' | symptom2=='Hangnail' | symptom3=='Hangnail'])
summary(Symptoms)
#Frequency table sex*treatment, sex*Symptoms
summary(sex ~ treatment + Symptoms, fun=table)
# Check:
ma <- inmChoice(Symptoms, 'Muscle Ache')
table(sex[ma])
# could also do:
# summary(sex ~ treatment + mChoice(symptom1,symptom2,symptom3), fun=table)
#Compute mean age, separately by 3 variables
summary(age ~ sex + treatment + Symptoms)
summary(age ~ sex + treatment + Symptoms, method="cross")
f <- summary(treatment ~ age + sex + Symptoms, method="reverse", test=TRUE)
f
# trio of numbers represent 25th, 50th, 75th percentile
print(f, long=TRUE)