subset.itemresp {psychotools}

Subsetting Item Response Data

Description

Subsetting and combining "itemresp" data objects.

Usage

  ## S3 method for class 'itemresp'
subset(x, items = NULL, subjects = NULL, ...)

Arguments

x

an object of class "itemresp".

items

character, integer, or logical for subsetting the items.

subjects

character, integer, or logical for subsetting the subjects.

...

currently not used.

Details

The subset method selects subsets of items and/or subjects in item response data. Alternatively, the [ method can be used with the row index corresponding to subjects and the column index corresponding to items.

The c method can be used to combine item response data from different subjects for the same items

The merge method can be used to combine item response data from the same subjects for different items.

See Also

itemresp

Examples

## binary responses to three items, coded as matrix
x <- cbind(c(1, 0, 1, 0), c(1, 0, 0, 0), c(0, 1, 1, 1))
xi <- itemresp(x)

## subsetting/indexing
xi[2]
xi[-(3:4)]
xi[c(TRUE, TRUE, FALSE, FALSE)]
subset(xi, items = 1:2) # or xi[, 1:2]
subset(xi, items = -2, subjects = 2:3)

## combine two itemresp vectors for different subjects but the same items
xi12 <- xi[1:2]
xi34 <- xi[3:4]
c(xi12, xi34)

## combine two itemresp vectors for the same subjects but different items
## polytomous responses in a data frame
d <- data.frame(q1 = c(-2, 1, -1, 0), q2 = factor(c(1, 3, 1, 3),
  levels = 1:3, labels = c("disagree", "neutral", "agree")))
di <-itemresp(d)
merge(xi, di)

## if subjects have names/IDs, these are used for merging
names(xi) <- c("John", "Joan", "Jen", "Jim")
names(di) <-         c("Joan", "Jen", "Jim", "Jo")
merge(xi, di)
merge(xi, di, all = TRUE)