| pretty {base} | R Documentation |
Compute a sequence of about n+1 equally spaced nice 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.
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)
x |
numeric vector |
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 numeric
by a 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. |
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.
.........
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
axTicks for the computation of pretty axis tick
locations in plots, particularly on the log scale.
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}
str(lapply(add.names(-10:20), pretty))
str(lapply(add.names(0:20), pretty, min = 0))
sapply( add.names(0:20), pretty, min = 4)
pretty(1.234e100)
pretty(1001.1001)
pretty(1001.1001, shrink = .2)
for(k in -7:3)
cat("shrink=",formatC(2^k,wid=9),":",
formatC(pretty(1001.1001, shrink = 2^k), wid=6),"\n")