EdSurvey (version 1.0.6)

subset.edsurvey.data.frame: Subset the rows of an edsurvey.data.frame.

Description

Return a new edsurvey.data.frame which, when passed to getData, returns only a subset of the data.

Usage

# S3 method for edsurvey.data.frame
subset(x, subset, ..., inside = FALSE)
# S4 method for edsurvey.data.frame
subset(x, subset, ..., inside = FALSE)
# S4 method for light.edsurvey.data.frame
subset(x, subset, ..., inside = FALSE)

Arguments

x

an edsurvey.data.frame.

subset

a condition, written out similar to summary; when inside=TRUE, parsed text.

...

not used. Included only for compatability.

inside

set to TRUE to prevent substitute from being called on the subset argument, see Details.

Value

An object of the same class as x (an edsurvey.data.frame or a light.edsurvey.data.frame).

Details

Note that any variables defined in condition that are not references to column names on the edsurvey.data.frame and are part of the environment where subset.edsurvey.data.frame was called will be evaluated in the environment from which subset.edsurvey.data.frame was called. Similar to the difficulty of using subset within a function call because of the call to substitute on condition, this function is difficult to use (with inside set to the default value of FALSE) inside another function call. See examples for how to call this function from within another function.

References

Wickham, H. (2014). Advanced R. Boca Raton, FL: Chapman & Hall/CRC.

Examples

# NOT RUN {
# read in the example data (generated, not real student data)
sdf <- readNAEP(system.file("extdata/data", "M36NT2PM.dat", package = "NAEPprimer"))

# table to compare to subsequent tables with subsets:
edsurveyTable(composite ~ dsex, data=sdf, returnMeans=FALSE, returnSepct=FALSE)

# subset to just males
newsdf <-  subset(x=sdf, subset= dsex == "Male") 
# table of dsex after subset
edsurveyTable(composite ~ dsex, data=newsdf, returnMeans=FALSE, returnSepct=FALSE)

# Variable names that are not in the sdf get resolved in the parent frame.
# Practically, that means that the following two subset 
# calls sdfM1 and sdfM2 do the same thing:
male_var <- "Male"
sdfM1 <- subset(x=sdf, subset= dsex == male_var)
sdfM2 <- subset(x=sdf, subset= dsex == "Male")
table(getData(data=sdfM1, varnames="dsex"))
table(getData(data=sdfM2, varnames="dsex"))

# variable can also be resolved as members of lists
genders <- c("Male", "Female","not a sex level")
sdfn <- subset(x=sdf, subset= dsex == genders[2]) 
table(getData(data=sdfn, varnames="dsex"))

# variables can also be subset using %in%
sdfM3 <- subset(x=sdf, subset= dsex %in% c("Male", "not a sex level")) 
table(getData(data=sdfM3, varnames="dsex"))

# if you need to call a name on the sdf dynamically, you can use as.name
dsex_standin <- as.name("dsex")
sdfM4 <- subset(x=sdf, subset= dsex_standin == "Male")
table(getData(data=sdfM4, varnames="dsex"))


# Here is an example of how one might want to call
# subset from within a function or loop.
# First,define a few variables to use dynamically
rhs_vars <- c("dsex", "b017451")
lvls <- c("Male", "Female")

# create a parsed condition
cond <- parse(text=paste0(rhs_vars[1], " == \"",lvls[1],"\""))[[1]]

# when inside=TRUE a parsed condition can be passed to subset
dsdf <- subset(x=sdf, subset=cond, inside=TRUE)

# check the result
table(getData(data=dsdf, varnames="dsex"))
# }