par: Set or Query Graphical Parameters

Set or Query Graphical Parameters

Description

par can be used to set or query graphical parameters. Parameters can be set by specifying them as arguments to par in tag = value form, or by passing them as a list of tagged values.

Usage

par(..., no.readonly = FALSE)

<highlevel plot> (..., <tag> = <value>)

Arguments

Details

Each device has its own set of graphical parameters. If the current device is the null device, par will open a new device before querying/setting parameters. (What device is controlled by options("device").)

Parameters are queried by giving one or more character vectors of parameter names to par.

par() (no arguments) or par(no.readonly = TRUE) is used to get all the graphical parameters (as a named list). Their names are currently taken from the unexported variable graphics:::.Pars.

R.O. indicates read-only arguments: These may only be used in queries and cannot be set. ("cin", "cra", "csi", "cxy", "din" and "page" are always read-only.)

Several parameters can only be set by a call to par():

• "ask",

• "fig", "fin",

• "lheight",

• "mai", "mar", "mex", "mfcol", "mfrow", "mfg",

• "new",

• "oma", "omd", "omi",

• "pin", "plt", "ps", "pty",

• "usr",

• "xlog", "ylog",

• "ylbias"

The remaining parameters can also be set as arguments (often via ...) to high-level plot functions such as plot.default, plot.window, points, lines, abline, axis, title, text, mtext, segments, symbols, arrows, polygon, rect, box, contour, filled.contour and image. Such settings will be active during the execution of the function, only. However, see the comments on bg, cex, col, lty, lwd and pch which may be taken as arguments to certain plot functions rather than as graphical parameters.

The meaning of ‘character size’ is not well-defined: this is set up for the device taking pointsize into account but often not the actual font family in use. Internally the corresponding pars (cra, cin, cxy and csi) are used only to set the inter-line spacing used to convert mar and oma to physical margins. (The same inter-line spacing multiplied by lheight is used for multi-line strings in text and strheight.)

Note that graphical parameters are suggestions: plotting functions and devices need not make use of them (and this is particularly true of non-default methods for e.g. plot).

Value

When parameters are set, their previous values are returned in an invisible named list. Such a list can be passed as an argument to par to restore the parameter values. Use par(no.readonly = TRUE) for the full list of parameters that can be restored. However, restoring all of these is not wise: see the ‘Note’ section.

When just one parameter is queried, the value of that parameter is returned as (atomic) vector. When two or more parameters are queried, their values are returned in a list, with the list names giving the parameters.

Note the inconsistency: setting one parameter returns a list, but querying one parameter returns a vector.

Graphical Parameters

adj

The value of adj determines the way in which text strings are justified in text, mtext and title. A value of 0 produces left-justified text, 0.5 (the default) centered text and 1 right-justified text. (Any value in [0, 1] is allowed, and on most devices values outside that interval will also work.)

Note that the adj argument of text also allows adj = c(x, y) for different adjustment in x- and y- directions. Note that whereas for text it refers to positioning of text about a point, for mtext and title it controls placement within the plot or device region.

ann

If set to FALSE, high-level plotting functions calling plot.default do not annotate the plots they produce with axis titles and overall titles. The default is to do annotation.

ask

logical. If TRUE (and the R session is interactive) the user is asked for input, before a new figure is drawn. As this applies to the device, it also affects output by packages grid and lattice. It can be set even on non-screen devices but may have no effect there.

This not really a graphics parameter, and its use is deprecated in favour of devAskNewPage.

bg

The color to be used for the background of the device region. When called from par() it also sets new = FALSE. See section ‘Color Specification’ for suitable values. For many devices the initial value is set from the bg argument of the device, and for the rest it is normally "white".

Note that some graphics functions such as plot.default and points have an argument of this name with a different meaning.

bty

A character string which determined the type of box which is drawn about plots. If bty is one of "o" (the default), "l", "7", "c", "u", or "]" the resulting box resembles the corresponding upper case letter. A value of "n" suppresses the box.

cex

A numerical value giving the amount by which plotting text and symbols should be magnified relative to the default. This starts as 1 when a device is opened, and is reset when the layout is changed, e.g. by setting mfrow.

Note that some graphics functions such as plot.default have an argument of this name which multiplies this graphical parameter, and some functions such as points and text accept a vector of values which are recycled.

cex.axis

The magnification to be used for axis annotation relative to the current setting of cex.

cex.lab

The magnification to be used for x and y labels relative to the current setting of cex.

cex.main

The magnification to be used for main titles relative to the current setting of cex.

cex.sub

The magnification to be used for sub-titles relative to the current setting of cex.

cin

R.O.; character size (width, height) in inches. These are the same measurements as cra, expressed in different units.

col

A specification for the default plotting color. See section ‘Color Specification’.

Some functions such as lines and text accept a vector of values which are recycled and may be interpreted slightly differently.

col.axis

The color to be used for axis annotation. Defaults to "black".

col.lab

The color to be used for x and y labels. Defaults to "black".

col.main

The color to be used for plot main titles. Defaults to "black".

col.sub

The color to be used for plot sub-titles. Defaults to "black".

cra

R.O.; size of default character (width, height) in ‘rasters’ (pixels). Some devices have no concept of pixels and so assume an arbitrary pixel size, usually 1/72 inch. These are the same measurements as cin, expressed in different units.

crt

A numerical value specifying (in degrees) how single characters should be rotated. It is unwise to expect values other than multiples of 90 to work. Compare with srt which does string rotation.

csi

R.O.; height of (default-sized) characters in inches. The same as par("cin")[2].

cxy

R.O.; size of default character (width, height) in user coordinate units. par("cxy") is par("cin")/par("pin") scaled to user coordinates. Note that c(strwidth(ch), strheight(ch)) for a given string ch is usually much more precise.

din

R.O.; the device dimensions, (width, height), in inches. See also dev.size, which is updated immediately when an on-screen device windows is re-sized.

err

(Unimplemented; R is silent when points outside the plot region are not plotted.) The degree of error reporting desired.

family

The name of a font family for drawing text. The maximum allowed length is 200 bytes. This name gets mapped by each graphics device to a device-specific font description. The default value is "" which means that the default device fonts will be used (and what those are should be listed on the help page for the device). Standard values are "serif", "sans" and "mono", and the Hershey font families are also available. (Devices may define others, and some devices will ignore this setting completely. Names starting with "Hershey" are treated specially and should only be used for the built-in Hershey font families.) This can be specified inline for text.

fg

The color to be used for the foreground of plots. This is the default color used for things like axes and boxes around plots. When called from par() this also sets parameter col to the same value. See section ‘Color Specification’. A few devices have an argument to set the initial value, which is otherwise "black".

fig

A numerical vector of the form c(x1, x2, y1, y2) which gives the (NDC) coordinates of the figure region in the display region of the device. If you set this, unlike S, you start a new plot, so to add to an existing plot use new = TRUE as well.

fin

The figure region dimensions, (width, height), in inches. If you set this, unlike S, you start a new plot.

font

An integer which specifies which font to use for text. If possible, device drivers arrange so that 1 corresponds to plain text (the default), 2 to bold face, 3 to italic and 4 to bold italic. Also, font 5 is expected to be the symbol font, in Adobe symbol encoding. On some devices font families can be selected by family to choose different sets of 5 fonts.

font.axis

The font to be used for axis annotation.

font.lab

The font to be used for x and y labels.

font.main

The font to be used for plot main titles.

font.sub

The font to be used for plot sub-titles.

lab

A numerical vector of the form c(x, y, len) which modifies the default way that axes are annotated. The values of x and y give the (approximate) number of tickmarks on the x and y axes and len specifies the label length. The default is c(5, 5, 7). Note that this only affects the way the parameters xaxp and yaxp are set when the user coordinate system is set up, and is not consulted when axes are drawn. len is unimplemented in R.

las

numeric in {0,1,2,3}; the style of axis labels.

0:

always parallel to the axis [default],

1:

always horizontal,

2:

always perpendicular to the axis,

3:

always vertical.

Also supported by mtext. Note that string/character rotation via argument srt to par does not affect the axis labels.

lend

The line end style. This can be specified as an integer or string:

0

and "round" mean rounded line caps [default];

1

and "butt" mean butt line caps;

2

and "square" mean square line caps.

lheight

The line height multiplier. The height of a line of text (used to vertically space multi-line text) is found by multiplying the character height both by the current character expansion and by the line height multiplier. Default value is 1. Used in text and strheight.

ljoin

The line join style. This can be specified as an integer or string:

0

and "round" mean rounded line joins [default];

1

and "mitre" mean mitred line joins;

2

and "bevel" mean bevelled line joins.

lmitre

The line mitre limit. This controls when mitred line joins are automatically converted into bevelled line joins. The value must be larger than 1 and the default is 10. Not all devices will honour this setting.

lty

The line type. Line types can either be specified as an integer (0=blank, 1=solid (default), 2=dashed, 3=dotted, 4=dotdash, 5=longdash, 6=twodash) or as one of the character strings "blank", "solid", "dashed", "dotted", "dotdash", "longdash", or "twodash", where "blank" uses ‘invisible lines’ (i.e., does not draw them).

Alternatively, a string of up to 8 characters (from c(1:9, "A":"F")) may be given, giving the length of line segments which are alternatively drawn and skipped. See section ‘Line Type Specification’.

Functions such as lines and segments accept a vector of values which are recycled.

lwd

The line width, a positive number, defaulting to 1. The interpretation is device-specific, and some devices do not implement line widths less than one. (See the help on the device for details of the interpretation.)

Functions such as lines and segments accept a vector of values which are recycled: in such uses lines corresponding to values NA or NaN are omitted. The interpretation of 0 is device-specific.

mai

A numerical vector of the form c(bottom, left, top, right) which gives the margin size specified in inches.

mar

A numerical vector of the form c(bottom, left, top, right) which gives the number of lines of margin to be specified on the four sides of the plot. The default is c(5, 4, 4, 2) + 0.1.

mex

mex is a character size expansion factor which is used to describe coordinates in the margins of plots. Note that this does not change the font size, rather specifies the size of font (as a multiple of csi) used to convert between mar and mai, and between oma and omi.

This starts as 1 when the device is opened, and is reset when the layout is changed (alongside resetting cex).

mfcol, mfrow

A vector of the form c(nr, nc). Subsequent figures will be drawn in an nr-by-nc array on the device by columns (mfcol), or rows (mfrow), respectively.

In a layout with exactly two rows and columns the base value of "cex" is reduced by a factor of 0.83: if there are three or more of either rows or columns, the reduction factor is 0.66.

Setting a layout resets the base value of cex and that of mex to 1.

If either of these is queried it will give the current layout, so querying cannot tell you the order in which the array will be filled.

Consider the alternatives, layout and split.screen.

mfg

A numerical vector of the form c(i, j) where i and j indicate which figure in an array of figures is to be drawn next (if setting) or is being drawn (if enquiring). The array must already have been set by mfcol or mfrow.

For compatibility with S, the form c(i, j, nr, nc) is also accepted, when nr and nc should be the current number of rows and number of columns. Mismatches will be ignored, with a warning.

mgp

The margin line (in mex units) for the axis title, axis labels and axis line. Note that mgp[1] affects title whereas mgp[2:3] affect axis. The default is c(3, 1, 0).

mkh

The height in inches of symbols to be drawn when the value of pch is an integer. Completely ignored in R.

new

logical, defaulting to FALSE. If set to TRUE, the next high-level plotting command (actually plot.new) should not clean the frame before drawing as if it were on a new device. It is an error (ignored with a warning) to try to use new = TRUE on a device that does not currently contain a high-level plot.

oma

A vector of the form c(bottom, left, top, right) giving the size of the outer margins in lines of text.

omd

A vector of the form c(x1, x2, y1, y2) giving the region inside outer margins in NDC (= normalized device coordinates), i.e., as a fraction (in [0, 1]) of the device region.

omi

A vector of the form c(bottom, left, top, right) giving the size of the outer margins in inches.

page

R.O.; A boolean value indicating whether the next call to plot.new is going to start a new page. This value may be FALSE if there are multiple figures on the page.

pch

Either an integer specifying a symbol or a single character to be used as the default in plotting points. See points for possible values and their interpretation. Note that only integers and single-character strings can be set as a graphics parameter (and not NA nor NULL).

Some functions such as points accept a vector of values which are recycled.

pin

The current plot dimensions, (width, height), in inches.

plt

A vector of the form c(x1, x2, y1, y2) giving the coordinates of the plot region as fractions of the current figure region.

ps

integer; the point size of text (but not symbols). Unlike the pointsize argument of most devices, this does not change the relationship between mar and mai (nor oma and omi).

What is meant by ‘point size’ is device-specific, but most devices mean a multiple of 1bp, that is 1/72 of an inch.

pty

A character specifying the type of plot region to be used; "s" generates a square plotting region and "m" generates the maximal plotting region.

smo

(Unimplemented) a value which indicates how smooth circles and circular arcs should be.

srt

The string rotation in degrees. See the comment about crt. Only supported by text.

tck

The length of tick marks as a fraction of the smaller of the width or height of the plotting region. If tck >= 0.5 it is interpreted as a fraction of the relevant side, so if tck = 1 grid lines are drawn. The default setting (tck = NA) is to use tcl = -0.5.

tcl

The length of tick marks as a fraction of the height of a line of text. The default value is -0.5; setting tcl = NA sets tck = -0.01 which is S' default.

usr

A vector of the form c(x1, x2, y1, y2) giving the extremes of the user coordinates of the plotting region. When a logarithmic scale is in use (i.e., par("xlog") is true, see below), then the x-limits will be 10 ^ par("usr")[1:2]. Similarly for the y-axis.

xaxp

A vector of the form c(x1, x2, n) giving the coordinates of the extreme tick marks and the number of intervals between tick-marks when par("xlog") is false. Otherwise, when log coordinates are active, the three values have a different meaning: For a small range, n is negative, and the ticks are as in the linear case, otherwise, n is in 1:3, specifying a case number, and x1 and x2 are the lowest and highest power of 10 inside the user coordinates, 10 ^ par("usr")[1:2]. (The "usr" coordinates are log10-transformed here!)

n = 1

will produce tick marks at 10^j for integer j,

n = 2

gives marks k 10^j with k in {1,5},

n = 3

gives marks k 10^j with k in {1,2,5}.

See axTicks() for a pure R implementation of this.

This parameter is reset when a user coordinate system is set up, for example by starting a new page or by calling plot.window or setting par("usr"): n is taken from par("lab"). It affects the default behaviour of subsequent calls to axis for sides 1 or 3.

It is only relevant to default numeric axis systems, and not for example to dates.

xaxs

The style of axis interval calculation to be used for the x-axis. Possible values are "r", "i", "e", "s", "d". The styles are generally controlled by the range of data or xlim, if given.
Style "r" (regular) first extends the data range by 4 percent at each end and then finds an axis with pretty labels that fits within the extended range.
Style "i" (internal) just finds an axis with pretty labels that fits within the original data range.
Style "s" (standard) finds an axis with pretty labels within which the original data range fits.
Style "e" (extended) is like style "s", except that it is also ensures that there is room for plotting symbols within the bounding box.
Style "d" (direct) specifies that the current axis should be used on subsequent plots.
(Only "r" and "i" styles have been implemented in R.)

xaxt

A character which specifies the x axis type. Specifying "n" suppresses plotting of the axis. The standard value is "s": for compatibility with S values "l" and "t" are accepted but are equivalent to "s": any value other than "n" implies plotting.

xlog

A logical value (see log in plot.default). If TRUE, a logarithmic scale is in use (e.g., after plot(*, log = "x")). For a new device, it defaults to FALSE, i.e., linear scale.

xpd

A logical value or NA. If FALSE, all plotting is clipped to the plot region, if TRUE, all plotting is clipped to the figure region, and if NA, all plotting is clipped to the device region. See also clip.

yaxp

A vector of the form c(y1, y2, n) giving the coordinates of the extreme tick marks and the number of intervals between tick-marks unless for log coordinates, see xaxp above.

yaxs

The style of axis interval calculation to be used for the y-axis. See xaxs above.

yaxt

A character which specifies the y axis type. Specifying "n" suppresses plotting.

ylbias

A positive real value used in the positioning of text in the margins by axis and mtext. The default is in principle device-specific, but currently 0.2 for all of R's own devices. Set this to 0.2 for compatibility with R < 2.14.0 on x11 and windows() devices.

ylog

A logical value; see xlog above.

Color Specification

Colors can be specified in several different ways. The simplest way is with a character string giving the color name (e.g., "red"). A list of the possible colors can be obtained with the function colors. Alternatively, colors can be specified directly in terms of their RGB components with a string of the form "#RRGGBB" where each of the pairs RR, GG, BB consist of two hexadecimal digits giving a value in the range 00 to FF. Colors can also be specified by giving an index into a small table of colors, the palette: indices wrap round so with the default palette of size 8, 10 is the same as 2. This provides compatibility with S. Index 0 corresponds to the background color. Note that the palette (apart from 0 which is per-device) is a per-session setting.

Negative integer colours are errors.

Additionally, "transparent" is transparent, useful for filled areas (such as the background!), and just invisible for things like lines or text. In most circumstances (integer) NA is equivalent to "transparent" (but not for text and mtext).

Semi-transparent colors are available for use on devices that support them.

The functions rgb, hsv, hcl, gray and rainbow provide additional ways of generating colors.

Line Type Specification

Line types can either be specified by giving an index into a small built-in table of line types (1 = solid, 2 = dashed, etc, see lty above) or directly as the lengths of on/off stretches of line. This is done with a string of an even number (up to eight) of characters, namely non-zero (hexadecimal) digits which give the lengths in consecutive positions in the string. For example, the string "33" specifies three units on followed by three off and "3313" specifies three units on followed by three off followed by one on and finally three off. The ‘units’ here are (on most devices) proportional to lwd, and with lwd = 1 are in pixels or points or 1/96 inch.

The five standard dash-dot line types (lty = 2:6) correspond to c("44", "13", "1343", "73", "2262").

Note that NA is not a valid value for lty.

Note

The effect of restoring all the (settable) graphics parameters as in the examples is hard to predict if the device has been resized. Several of them are attempting to set the same things in different ways, and those last in the alphabet will win. In particular, the settings of mai, mar, pin, plt and pty interact, as do the outer margin settings, the figure layout and figure region size.

References

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

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

See Also

plot.default for some high-level plotting parameters; colors; clip; options for other setup parameters; graphic devices x11, postscript and setting up device regions by layout and split.screen.

Examples

op <- par(mfrow = c(2, 2), # 2 x 2 pictures on one plot
          pty = "s")       # square plotting region,
                           # independent of device size

## At end of plotting, reset to previous settings:
par(op)

## Alternatively,
op <- par(no.readonly = TRUE) # the whole list of settable par's.
## do lots of plotting and par(.) calls, then reset:
par(op)
## Note this is not in general good practice

par("ylog") # FALSE
plot(1 : 12, log = "y")
par("ylog") # TRUE

plot(1:2, xaxs = "i") # 'inner axis' w/o extra space
par(c("usr", "xaxp"))

( nr.prof <-
c(prof.pilots = 16, lawyers = 11, farmers = 10, salesmen = 9, physicians = 9,
  mechanics = 6, policemen = 6, managers = 6, engineers = 5, teachers = 4,
  housewives = 3, students = 3, armed.forces = 1))
par(las = 3)
barplot(rbind(nr.prof)) # R 0.63.2: shows alignment problem
par(las = 0)  # reset to default

require(grDevices) # for gray
## 'fg' use:
plot(1:12, type = "b", main = "'fg' : axes, ticks and box in gray",
     fg = gray(0.7), bty = "7" , sub = R.version.string)

ex <- function() {
   old.par <- par(no.readonly = TRUE) # all par settings which
                                      # could be changed.
   on.exit(par(old.par))
   ## ...
   ## ... do lots of par() settings and plots
   ## ...
   invisible() #-- now,  par(old.par)  will be executed
}
ex()

## Line types
showLty <- function(ltys, xoff = 0, ...) {
   stopifnot((n <- length(ltys)) >= 1)
   op <- par(mar = rep(.5,4)); on.exit(par(op))
   plot(0:1, 0:1, type = "n", axes = FALSE, ann = FALSE)
   y <- (n:1)/(n+1)
   clty <- as.character(ltys)
   mytext <- function(x, y, txt)
      text(x, y, txt, adj = c(0, -.3), cex = 0.8, ...)
   abline(h = y, lty = ltys, ...); mytext(xoff, y, clty)
   y <- y - 1/(3*(n+1))
   abline(h = y, lty = ltys, lwd = 2, ...)
   mytext(1/8+xoff, y, paste(clty," lwd = 2"))
}
showLty(c("solid", "dashed", "dotted", "dotdash", "longdash", "twodash"))
par(new = TRUE)  # the same:
showLty(c("solid", "44", "13", "1343", "73", "2262"), xoff = .2, col = 2)
showLty(c("11", "22", "33", "44",   "12", "13", "14",   "21", "31"))