R: Pretty Breakpoints

pretty {base} | R Documentation

## Pretty Breakpoints

### Description

Compute a sequence of about `n+1` equally spaced ‘round’ values which cover the range of the values in `x`. The values are chosen so that they are 1, 2 or 5 times a power of 10.

### Usage

    pretty(x, ...)

    ## Default S3 method:
    pretty(x, n = 5, min.n = n %/% 3,  shrink.sml = 0.75,
           high.u.bias = 1.5, u5.bias = .5 + 1.5*high.u.bias,
           eps.correct = 0, ...)

### Arguments

`x` | an object coercible to numeric by `as.numeric`.
`n` | integer giving the desired number of intervals. Non-integer values are rounded down.
`min.n` | nonnegative integer giving the minimal number of intervals. If `min.n == 0`, `pretty(.)` may return a single value.
`shrink.sml` | positive number, a factor (smaller than one) by which a default scale is shrunk in the case when `range(x)` is very small (usually 0).
`high.u.bias` | non-negative numeric, typically > 1. The interval unit is determined as {1,2,5,10} times `b`, a power of 10. Larger `high.u.bias` values favor larger units.
`u5.bias` | non-negative numeric multiplier favoring factor 5 over 2. Default and ‘optimal’: `u5.bias = .5 + 1.5*high.u.bias`.
`eps.correct` | integer code, one of {0,1,2}. If non-0, an epsilon correction is made at the boundaries such that the result boundaries will be outside `range(x)`; in the small case, the correction is only done if `eps.correct >= 2`.
`...` | further arguments for methods.

### Details

`pretty` ignores non-finite values in `x`.

Let `d <- max(x) - min(x)` ≥ 0. If `d` is not (very close) to 0, we let `c <- d/n`, otherwise more or less `c <- max(abs(range(x)))*shrink.sml / min.n`. Then, the 10 base `b` is 10^(floor(log10(c))) such that b ≤ c < 10b.

Now determine the basic unit u as one of {1,2,5,10} b, depending on c/b in [1,10) and the two ‘bias’ coefficients, h =`high.u.bias` and f =`u5.bias`.

.........

### References

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

### See Also

`axTicks` for the computation of pretty axis tick locations in plots, particularly on the log scale.

### Examples

    pretty(1:15)          # 0  2  4  6  8 10 12 14 16
    pretty(1:15, h = 2)   # 0  5 10 15
    pretty(1:15, n = 4)   # 0  5 10 15
    pretty(1:15 * 2)      # 0  5 10 15 20 25 30
    pretty(1:20)          # 0  5 10 15 20
    pretty(1:20, n = 2)   # 0 10 20
    pretty(1:20, n = 10)  # 0  2  4 ... 20

    for(k in 5:11) {
      cat("k=", k, ": "); print(diff(range(pretty(100 + c(0, pi*10^-k)))))}

    ##-- more bizarre, when  min(x) == max(x):
    pretty(pi)

    add.names <- function(v) { names(v) <- paste(v); v}
    utils::str(lapply(add.names(-10:20), pretty))
    utils::str(lapply(add.names(0:20),   pretty, min.n = 0))
    sapply(    add.names(0:20),   pretty, min.n = 4)

    pretty(1.234e100)
    pretty(1001.1001)
    pretty(1001.1001, shrink = 0.2)
    for(k in -7:3)
      cat("shrink=", formatC(2^k, width = 9),":",
          formatC(pretty(1001.1001, shrink.sml = 2^k), width = 6),"\n")

[Package base version 4.0.5 Index]