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Add Error Bars to an Existing Plot

Source: R/errBars.R
errBars.Rd

Add vertical or horizontal error bars to an existing plot.

Usage

errBars(from, to = NULL, pos = NULL, horiz = TRUE, points = NULL, ...)

Arguments

from

coordinates of the lower end of the error bars.

If to = NULL and from is a matrix:

  • a 2-column matrix is interpreted as cbind(from, to)

  • a 3-column matrix is interpreted as cbind(point, from, to)

to

coordinates of the upper end of the error bars.

pos

position of the error bars.

For vertical bars this corresponds to x-positions; for horizontal bars to y-positions.

horiz

logical; if TRUE, horizontal error bars are drawn.

points

optional point specification.

...

additional graphical arguments passed to arrows().

Value

Invisibly returns a list with components:

from

Lower endpoints

to

Upper endpoints

pos

Positions of the error bars

points

Point coordinates

Details

This is a lightweight wrapper around arrows() with optional point symbols added via points().

Additional graphical arguments in ... are passed to arrows() and may be used to control the appearance of the error bars.

Common examples include:

  • col: line color

  • lwd: line width

  • lty: line type

  • code: which end caps to draw

  • length: length of the end caps

Point symbols may optionally be added:

  • points = TRUE: draw default points halfway between from and to

  • points = numeric: use these values as point coordinates

  • points = list(...): fully specify point coordinates and graphical parameters

Example:


points = list(
  val = estimate,
  pch = 21,
  bg  = "gold",
  col = "black",
  cex = 1.2
)

The default orientation is horizontal (horiz = TRUE), which suits the typical use case of adding confidence intervals to a dotchart(). Set horiz = FALSE for vertical bars on barplots or similar.

See also

arrows(), points()

Other graphics.annotation: barText(), boxedText(), colLegend(), stamp(), textLegend(), titleRect()

Examples

op <- par(no.readonly = TRUE)
par(mfrow = c(2, 2))

b <- barplot(1:5, ylim = c(0, 6))

errBars(
  from = 1:5 - 0.5,
  to = 1:5 + 0.5,
  pos = b,
  length = 0.15
)

# midpoint symbols
b <- barplot(1:5, ylim = c(0, 6))

errBars(
  from = 1:5 - 0.5,
  to = 1:5 + 0.5,
  pos = b,
  points = TRUE
)

# custom points
dotchart(1:5, xlim = c(0, 6))

errBars(
  from = 1:5 - 0.2,
  to = 1:5 + 0.2,
  horiz = TRUE,
  points = list(
    val = 1:5,
    pch = 21,
    bg = "gold",
    col = "black",
    cex = 1.2
  )
)

par(op)