R: Identify Points in a Scatter Plot

identify {base} | R Documentation

## Identify Points in a Scatter Plot

### Description

`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 to the pointer, its index will be returned as part of the value of the call.

### Usage

    identify(x, ...)
    identify.default(x, y = NULL, labels = seq(along = x), pos = FALSE,
                     n = length(x), plot = TRUE, offset = 0.5, ...)

### Arguments

`x,y` | coordinates of points in a scatter plot. Alternatively, any object which defines coordinates (a plotting structure, time series etc.) can be given as `x` and `y` left undefined.
`labels` | an optional vector, the same length as `x` and `y`, giving labels for the points.
`pos` | if `pos` is `TRUE`, a component is added to the return value which indicates where text was plotted relative to each identified point (1=below, 2=left, 3=above and 4=right).
`n` | the maximum number of points to be identified.
`plot` | if `plot` is `TRUE`, the labels are printed at the points and if `FALSE` they are omitted.
`offset` | the distance (in character widths) which separates the label from identified points.
`...` | further arguments to `par(.)`.

### Details

If in addition, `plot` is `TRUE`, the point is labelled with the corresponding element of `text`.

The labels are placed either below, to the left, above or to the right of the identified point, depending on where the cursor was.

The identification process is terminated by pressing any mouse button other than the first.

If the window is resized or hidden and then exposed before the identification process has terminated, any labels drawn by `identify` will disappear. These will reappear once the identification process has terminated and the window is resized or hidden and exposed again. This is because the labels drawn by `identify` are not recorded in the device's display list until the identification process has terminated.

### Value

If `pos` is `FALSE`, an integer vector containing the indexes of the identified points.
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.

### See Also

`locator`

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