R: Compute Axis Tickmark Locations

axTicks {graphics} | R Documentation

## Compute Axis Tickmark Locations

### Description

Compute pretty tickmark locations, the same way as R does internally. This is only non-trivial when log coordinates are active. By default, gives the `at` values which `axis(side)` would use.

### Usage

    axTicks(side, axp = NULL, usr = NULL, log = NULL)

### Arguments

`side` | integer in 1:4, as for `axis`.
`axp` | numeric vector of length three, defaulting to `par("xaxp")` or `par("yaxp")` depending on the `side` argument.
`usr` | numeric vector of length four, defaulting to `par("usr")` giving horizontal (‘x’) and vertical (‘y’) user coordinate limits.
`log` | logical indicating if log coordinates are active; defaults to `par("xlog")` or `par("ylog")`.

### Details

The `axp`, `usr`, and `log` arguments must be consistent as their default values (the `par(..)` results) are. If you specify all three (as non-NULL), the graphics environment is not used at all. Note that the meaning of `axp` alters very much when `log` is `TRUE`, see the documentation on `par(xaxp=.)`.

`axTicks()` can be regarded as an R implementation of the C function `CreateAtVector()` in ‘..../src/main/plot.c’ which is called by `axis(side,*)` when no argument `at` is specified.

### Value

numeric vector of coordinate values at which axis tickmarks can be drawn. By default, when only the first argument is specified, these values should be identical to those that `axis(side)` would use or has used.

### See Also

`axis`, `par`. `pretty` uses the same algorithm (but independently of the graphics environment) and has more options. However it is not available for `log = TRUE.`

### Examples

     plot(1:7, 10*21:27)
     axTicks(1)
     axTicks(2)
     stopifnot(identical(axTicks(1), axTicks(3)),
               identical(axTicks(2), axTicks(4)))

    ## Show how axTicks() and axis() correspond :
    op <- par(mfrow = c(3,1))
    for(x in 9999*c(1,2,8)) {
        plot(x,9, log = "x")
        cat(formatC(par("xaxp"), width=5),";", T <- axTicks(1),"\n")
        rug(T, col="red")
    }
    par(op)

[Package graphics version 2.8.1 Index]