identify {graphics}R Documentation

Identify Points in a Scatter Plot


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.


identify(x, ...)

## Default S3 method:
identify(x, y = NULL, labels = seq(along = x), pos = FALSE,
         n = length(x), plot = TRUE, atpen = FALSE, offset = 0.5,
         tolerance = 0.25, ...)


x,y coordinates of points in a scatter plot. Alternatively, any object which defines coordinates (a plotting structure, time series etc: see xy.coords) can be given as x, and y left undefined.
labels an optional character vector, the same length as x and y, giving labels for the points. Will be coerced using as.character.
pos if pos is TRUE, a component is added to the return value which indicates where text was plotted relative to each identified point: see Value.
n the maximum number of points to be identified.
plot logical: if plot is TRUE, the labels are printed at the points and if FALSE they are omitted.
atpen logical: if TRUE and plot = TRUE, the lower-left corners of the labels are plotted at the points clicked rather than relative to the points.
offset the distance (in character widths) which separates the label from identified points. Ignored if atpen = TRUE or pos = 0.
tolerance the maximal distance (in inches) for the pointer to be ‘close enough’ to a point.
... further arguments passed to par such as cex, col and font.


identify is only supported on screen devices such as X11, windows and quartz. On other devices the call will do nothing.

If plot is TRUE, the point is labelled with the corresponding element of text. The labels are placed below, to the left, above or to the right of the identified point, depending on where the cursor was relative to the point.

For the usual X11 device the identification process is terminated by pressing any mouse button other than the first. For the quartz device the process is terminated by pressing the ESC key.

On most devices which support identify, successful selection of a point is indicated by a bell sound unless options(locatorBell = FALSE) has been set.

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.


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 (1=below, 2=left, 3=above, 4=right and 0=no offset, used if atpen = TRUE).


Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

See Also


[Package graphics version 2.5.0 Index]