Identify Points In a Plot Using a Formula

The function identify reads the position of the graphics pointer when the (first) mouse button is pressed. It then searches the coordinates given in x and y for the point closest to the pointer. If this point is close enough to the pointer, its index will be returned as part of the value of the call.

# S3 method for class 'formula'
identify (formula, data, subset, na.action, ...)

Arguments

formula

a formula of the form lhs ~ rhs where lhs gives the data values and rhs the corresponding groups.

data

The data frame from which the formula should be evaluated.

subset

an optional vector specifying a subset of observations to be used.

na.action

a function which indicates what should happen when the data contain NAs. Defaults to getOption("na.action").

...

Other arguments to be passed to identify.

Value

If pos is FALSE, an integer vector containing the indices of the identified points, in the order they were identified. If pos is TRUE, a list containing a component ind, indicating which points were identified and a component pos, indicating where the labels were placed relative to the identified points (1=below, 2=left, 3=above, 4=right and 0=no offset, used if atpen = TRUE).

Author

Derek Ogle <dogle@northland.edu>

Details

This function is meant to make it easier to call identify after plot has been called using a formula and the data argument.

A two dimensional plot must be active and the vectors in x and data frame in data must correspond to the x- and y-axes and the data of the plot.

Examples

if (FALSE) { # \dontrun{
## Copy and try in an interactive R session
plot(dist ~ speed, data = cars, subset = speed < 17)
identify(dist ~ speed, data = cars, subset = speed < 17)
} # }