grid {graphics}R Documentation

Add Grid to a Plot

Description

grid adds an nx by ny rectangular grid to an existing plot.

Usage

grid(nx = NULL, ny = nx, col = "lightgray", lty = "dotted",
     lwd = par("lwd"), equilogs = TRUE, nintLog = NULL)

Arguments

nx, ny

number of cells of the grid in x and y direction. When NULL, as per default, the grid aligns with the tick marks on the corresponding default axis (i.e., tickmarks as computed by axTicks). When NA, no grid lines are drawn in the corresponding direction.

col

character or (integer) numeric; color of the grid lines.

lty

character or (integer) numeric; line type of the grid lines.

lwd

non-negative numeric giving line width of the grid lines.

equilogs

logical, only used when log coordinates and alignment with the axis tick marks are active. Setting equilogs = FALSE in that case gives non equidistant tick aligned grid lines.

nintLog

one or two integers (or NULL), passed to axTicks() when nx or ny are to be determined; effective only with log coordinates.

Value

A list of the x ("atx") and y ("aty") coordinates at which the grid lines were drawn is returned invisibly.

Note

If more fine tuning is required, use abline(h = ., v = .) directly.

References

Murrell, P. (2005) R Graphics. Chapman & Hall/CRC Press.

See Also

plot, abline, lines, points.

Examples

plot(1:3)
grid(NA, 5, lwd = 2) # grid only in y-direction

## maybe change the desired number of tick marks:  par(lab = c(mx, my, 7))
op <- par(mfcol = 1:2)
with(iris,
     {
     plot(Sepal.Length, Sepal.Width, col = as.integer(Species),
          xlim = c(4, 8), ylim = c(2, 4.5), panel.first = grid(),
          main = "with(iris,  plot(...., panel.first = grid(), ..) )")
     plot(Sepal.Length, Sepal.Width, col = as.integer(Species),
          panel.first = grid(3, lty = 1, lwd = 2),
          main = "... panel.first = grid(3, lty = 1, lwd = 2), ..")
     }
    )
par(op)

plot(1:64)
gr <- grid() # now *invisibly* returns the grid "at" locations
str(gr)
stopifnot(length(gr) == 2, identical(gr[[1]], gr[[2]]),
          gr[["atx"]] == 10*(0:6))

## In log-scale plots :
plot(8:270, log="xy") ; grid() # at (1, 10, 100); if preferring "all" grid lines:
plot(8:270, log="xy") ; grid(equilogs = FALSE) -> grll
stopifnot(identical(grll, list(atx = c(1, 2, 5, 10, 20, 50, 100, 200),
                               aty = c(         10, 20, 50, 100, 200))))

x <- 2^(-9:70)
plot(log(x) ~ x, log="xy")
grll <- grid(equilogs = FALSE, col = adjustcolor("green", 1/3))
gr20 <- grid(nintLog = 20)
gr25 <- grid(nintLog = 25, col="thistle")
str(gr25)
stopifnot(exprs = {
    grll$aty == c(1, 2, 5, 10, 20, 50)
    length(gr20$atx) >= 20 # 24 effectively
    all.equal(10^(-3:22), gr25$atx, tol = 1e-15)  # even tol = 0
})
[Package graphics version 4.5.0 Index]