earth (version 5.3.0)

# expand.bpairs: Expand binomial-pair data from short to long form

## Description

Expand binomial-pair data from ``short'' to ``long'' form.

The short form specifies the response with two columns giving the numbers of successes and failures. Example short form:

```    survived died dose    sex
3    0   10   male
2    1   10 female
1    2   20   male
1    2   20 female
```

The long form specifies the response as single column of `TRUE`s and `FALSE`s. For example, the long form of the above data (spaces and comments added):

```    survived dose    sex
TRUE   10   male     # row 1 of short data: 0 died, 3 survived
TRUE   10   male
TRUE   10   maleFALSE   10 female     # row 2 of short data: 1 died, 2 survived
TRUE   10 female
TRUE   10 femaleFALSE   20   male     # row 3 of short data: 2 died, 1 survived
FALSE   20   male
TRUE   20   maleFALSE   20 female     # row 4 of short data: 2 died, 1 survived
FALSE   20 female
TRUE   20 female
```

In this example the total number of survived and died for each row in the short data is the same, but in general that need not be true.

## Usage

```# S3 method for formula
expand.bpairs(formula = stop("no 'formula' argument"), data = NULL, sort = FALSE, …)# S3 method for default
expand.bpairs(data = stop("no 'data' argument"), y = NULL, sort = FALSE, …)```

## Arguments

formula

Model formula such as `survived + died ~ dose + temp`.

data

Matrix or dataframe containing the data.

y

Model response. One of:

o Two column matrix or dataframe of binomial pairs e.g. `cbind(survived, died=20-survived)`

o Two-element numeric vector specifying the response columns in `data` e.g. `c(1,2)`

o Two-element character vector specifying the response column names in `data` e.g. `c("survived", "died")`. The full names must be used (partial matching isn't supported).

sort

Default `FALSE`. Use `TRUE` to sort the rows of the long data so it is returned in canonical form, independent of the row order of the short data. The long data is sorted on predictor values; predictors on the left take precedence in the sort order.

Unused, but provided for generic/method consistency.

## Value

A dataframe of the data in the long form, with expanded binomial pairs. The first column of the data will be the response column (a column of `TRUE`s and `FALSE`s).

Additionally, the returned value has two attached attributes:

`bpairs.index` A vector of row indices into the returned data. Can be used to reconstruct the short data from the long data (although this package does not yet provide a function to do so).

`ynames` Column names of the original response (a two-element character vector).

## Examples

```# NOT RUN {
survived <- c(3,2,1,1) # short data for demo (too short to build a real model)
died     <- c(0,1,2,2)
dose <- c(10,10,20,20)
sex  <- factor(c("male", "female", "male", "female"))

short.data <- data.frame(survived, died, dose, sex)

expand.bpairs(survived + died ~ ., short.data) # returns long form of the data

# expand.bpairs(data=short.data, y=cbind(survived, died)) # equivalent
# expand.bpairs(short.data, c(1,2))                       # equivalent
# expand.bpairs(short.data, c("survived", "died"))        # equivalent

# For example models, see the earth vignette
# section "Short versus long binomial data".
# }
```