R: Add Points to a Plot

points {graphics} | R Documentation

## Add Points to a Plot

### Description

`points` is a generic function to draw a sequence of points at the specified coordinates. The specified character(s) are plotted, centered at the coordinates.

### Usage

    points(x, ...)

    ## Default S3 method:
    points(x, y = NULL, type = "p", pch = par("pch"),
           col = par("col"), bg = NA, cex = 1, ...)

### Arguments

`x, y` | coordinate vectors of points to plot.
`type` | character indicating the type of plotting; actually any of the `type`s as in `plot`.
`pch` | plotting “character”, i.e., symbol to use. `pch` can either be a `character` or an integer code for a set of graphics symbols. The full set of S symbols is available with `pch=0:18`, see the last picture from `example(points)`, i.e., the examples below. In addition, there is a special set of R plotting symbols which can be obtained with `pch=19:25` and `21:25` can be colored and filled with different colors: `pch=19`: solid circle, `pch=20`: bullet (smaller circle), `pch=21`: circle, `pch=22`: square, `pch=23`: diamond, `pch=24`: triangle point-up, `pch=25`: triangle point down. Values `pch=26:32` are currently unused, and `pch=32:255` give the text symbol in the encoding in use (see `postscript`).
`col` | color code or name, see `par`.
`bg` | background (“fill”) color for open plot symbols
`cex` | character expansion: a numerical vector.
`...` | Further graphical parameters (see `plot.xy` and `par`) may also be supplied as arguments.

### Details

The coordinates can be passed in a plotting structure (a list with `x` and `y` components), a two-column matrix, a time series, .... See `xy.coords`.

Arguments `pch`, `col`, `bg` and `cex` can be vectors (which will be recycled as needed) giving a value for each point plotted. Points whose `x`, `y`, `pch`, `col` or `cex` value is `NA` are omitted from the plot.

Graphical parameters are permitted as arguments to this function.

### References

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

### See Also

`plot`, `lines`, and the underlying “primitive” `plot.xy`.

### Examples

    plot(-4:4, -4:4, type = "n")# setting up coord. system
    points(rnorm(200), rnorm(200), col = "red")
    points(rnorm(100)/2, rnorm(100)/2, col = "blue", cex = 1.5)

    op <- par(bg = "light blue")
    x <- seq(0,2*pi, len=51)
    ## something "between type='b' and type='o'":
    plot(x, sin(x), type="o", pch=21, bg=par("bg"), col = "blue", cex=.6,
     main='plot(..., type="o", pch=21, bg=par("bg"))')
    par(op)

    ##-------- Showing all the extra & some char graphics symbols ------------
    Pex <- 3 ## good for both .Device=="postscript" and "x11"
    ipch <- 1:(np <- 25+11); k <- floor(sqrt(np)); dd <- c(-1,1)/2
    rx <- dd + range(ix <- (ipch-1) %/% k)
    ry <- dd + range(iy <- 3 + (k-1)-(ipch-1) %% k)
    pch <- as.list(ipch)
    pch[25+ 1:11] <- as.list(c("*",".", "o","O","0","+","-",":","|","%","#"))
    plot(rx, ry, type="n", axes = FALSE, xlab = "", ylab = "",
         main = paste("plot symbols :  points (...  pch = *, cex =", Pex,")"))
    abline(v = ix, h = iy, col = "lightgray", lty = "dotted")
    for(i in 1:np) {
      pc <- pch[[i]]
      points(ix[i], iy[i], pch = pc, col = "red", bg = "yellow", cex = Pex)
      ## red symbols with a yellow interior (where available)
      text(ix[i] - .3, iy[i], pc, col = "brown", cex = 1.2)
    }

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