How Big is Your Graph?
An R Cheat Sheet
Introduction
All functions that open a device for graphics will have height and width arguments to control the size of the graph and a pointsize argument to control the relative font size. In knitr, you control the size of the graph with the chunk options, fig.width and fig.height. This sheet will help you with calculating the size of the graph and various parts of the graph within R.
Your graphics device
dev.size() (width, height)
par("din") (r.o.) (width, height) in inches
Both the dev.size function and the din argument of par will tell you the size of the graphics device. The dev.size function will report the size in
1. inches (units="in"), the default
2. centimeters (units="cm")
3. pixels (units="px")
Like several other par arguments, din is read only (r.o.) meaning that you can ask its current value (par("din")) but you cannot change it (par(din=c(5,7)) will fail).
mai[3] (in), nmar[3] (lines)
usr[c(2,4)] (user)
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-plt[1] (pet) -plt[2] (pet)
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— usr[c(1,3)] (user) mai[1] (in), mar[1] (lines) —
dev.size()[1] (in, cm, px), din[1] (in)
Your plot margins
par("mai") (bottom, left, top, right) in inches par("mar") (bottom, left, top, right) in lines
Margins provide you space for your axes, axis, labels, and titles.
A "line" is the amount of vertical space needed for a line of text.
If your graph has no axes or titles, you can remove the margins (and maximize the plotting region) with
par(mar=rep(0,4))
Your plotting region
par("pin") (width, height) in inches par("plt") (left, right, bottom, top) in pet
The pin argument par gives you the size of the plotting region (the size of the device minus the size of the margins) in inches.
The pit argument gives you the percentage of the device from the left/bottom edge up to the left edge of the plotting region, the right edge, the bottom edge, and the top edge. The first and third values are equivalent to the percentage of space devoted to the left and bottom margins. Subtract the second and fourth values from 1 to get the percentage of space devoted to the right and top margins.
Your x-y coordinates
parfusf) (xmin, ymin, xmax, ymax)
Your x-y coordinates are the values you use when plotting your data. This normally is not the same as the values you specified with the xlim and ylim arguments in plot. By default, R adds an extra 4% to the plotting range (see the dark green region on the figure) so that points right up on the edges of your plot do not get partially clipped. You can override this by setting xaxs="i" and/or the yaxs="i" in par.
Run parf'usr") to find the minimum X value, the maximum X value, the minimum Y value, and the maximum Y value. If you assign new values to usr, you will update the x-y coordinates to the new values.
Getting a square graph
parfpty")
You can produce a square graph manually by setting the width and height to the same value and setting the margins so that the sum of the top and bottom margins equal the sum of the left and right margins. But a much easier way is to specify pty="s", which adjusts the margins so that the size of the plotting region is always square, even if you resize the graphics window.
Converting units
For many applications, you need to be able to translate user coordinates to pixels or inches. There are some cryptic shortcuts, but the simplest way is to get the range in user coordinates and measure the proportion of the graphics device devoted to the plotting region.
user.range <- par("usr")[c(2,4)] -par("usr")[c(1,3)]
region.pet <- par("plt")[c(2,4)] -par("plt")[c(1,3)]
region.px <-
dev.size(units="px") * region.pet
px.per.xy <- region.px / user.range
To convert a horizontal or distance from the x-coordinate value to pixels, multiply by px.per.xy[1] To convert a vertical distance, multiply by region.px.per.xy[2] To convert a diagonal distance, you need to invoke Pyhthagoras.
a. px <- x.dist*px.per.xy[1]
b. px <- y.dist*px.per.xy[2]
c. px <- sqrt(a.pxA2+b.pxA2)
To rotate a string to match the slope of a line segment, you need to convert the distances to pixels, calculate the arctangent, and convert from radians to degrees.
segments(xO, yO, x1, y1) delta.x <- (x1 - xO) * px.per.xy[1] delta.y <- (y1 - yO) * px.per.xy[y] angle.radians <- atan2(delta.y, delta.x) angle.degrees <- angle.radians * 180 / pi text(x1, yl, "TEXT', srt=angle.degrees)
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Learn more at blog.pmean.com/cheatsheets ■ Updated: August 2017
Panels
Character and string sizes
If your fonts are too big or too small
par("fig") (width, height) in pet par("fin") (width, height) in inches
If you display multiple plots within a single graphics window (e.g., with the mfrow or mfcol arguments of par or with the layout function), then the fig and fin arguments will tell you the size of the current subplot window in percent or inches, respectively.
par("oma") (bottom, left, top, right) in lines par("omd") (bottom, left, top, right) in pet par("omi") (bottom, left, top, right) in inches
Each subplot will have margins specified by mai or mar, but no outer margin around the entire set of plots, unless you specify them using oma, omd, or omi. You can place text in the outer margins using the mtext function with the argument outer=TRUE.
par("mfg") (r, c) or (r, c, maxr, maxc)
The mfg argument of par will allow you to jump to a subplot in a particular row and column. If you query with par("mfg"), you will get the current row and column followed by the maximum row and column.
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strheightQ
The strheight functions will tell you the height of a specified string in inches (units="inches"), x-y user coordinates (units="user") or as a percentage of the graphics device (units="figure").
For a single line of text, strheight will give you the height of the letter "M". If you have a string with one of more linebreaks ("\n"), the strheight function will measure the height of the letter "M" plus the height of one or more additional lines. The height of a line is dependent on the line spacing, set by the Iheight argument of par. The default line height (lheight=1), corresponding to single spaced lines, produces a line height roughly 1.5 times the height of "M".
strwidthQ
The strwidth function will produce different widths to individual characters, representing the proportional spacing used by most fonts (a "W" using much more space than an "i"). For the width of a string, the strwidth function will sum up the lengths of the individual characters in the string.
par("cin") (r.o.) (width, height) in inches par("csi") (r.o.) height in inches par("cra") (r.o.) (width, height) in pixels par("cxy") (r.o.) (width, height) in xy coordinates
The single value returned by the csi argument of par gives you the height of a line of text in inches. The second of the two values returned by cin, era, and cxy gives you the height of a line, in inches, pixels, or xy (user) coordinates.
The first of the two values returned by the cin, era, and cxy arguments to par gives you the approximate width of a single character, in inches, pixels, or xy (user) coordinates. The width, very slightly smaller than the actual width of the letter "W", is a rough estimate at best and ignores the variable with of individual letters.
These values are useful, however, in providing fast ratios of the relative sizes of the differing units of measure
px.per.in <- par("cra") / par("cin") px.per.xy <- par("cra") / par("cxy") xy.per.in <- par("cxy") / par("cin")
oma[3] (lines), omd[3] (pet), omi[3] (in)
mfg=c(1,1)
mfg=c<1,2)
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strheight("M")
— strheight("M\nM")
mfg=c(2,1)
,f7 mfg=c<2,2)
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Kim DO     F strheight(mnM\nM") cin[2] or csi (in), cra[2] (px), cxy[2] (user)
W     L      v i
strwi(X("W")    T    strwidth("v") I
strwidlh("L") strwicfth(V)
Li     v j
fct.
fig[1](pct) fin[1].(in)..
. I— oma[1] (lines), omd[1] (pet), omi[1] (in) .
CC BY Steve Simon, P.Mean Consulting ■ mailOpmean.com ■ https://www.rstudio.com/resources/cheatsheets/
cin[1] (in), cra[1] (px), cxy[1] (user)
Fixing this takes a bit of trial and error.
1. Specify a larger/smaller value for the pointsize argument when you open your graphics device.
2. Trying opening your graphics device with different values for height and width. Fonts that look too big might be better proportioned in a larger graphics window.
3. Use the cex argument to increase or decrease the relative size of your fonts.
If your axes don't fit
There are several possible solutions.
1. You can assign wider margins using the mar or mai argument in par.
2. You can change the orientation of the axis labels with las. Choose among
a. las=0 both axis labels parallel
b. Ias=1 both axis labels horizontal
c. Ias=2 both axis labels perpendicular
d. Ias=3 both axis labels vertical.
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3. change the relative size of the font
a. cex.axis for the tick mark labels.
b. cex.lab for xlab and ylab.
c. cex.main for the main title
d. cex.sub for the subtitle.
cex.axis cex.lab cex.sub
Learnmoreatblog.pmean.com/cheatsheets ■ Updated: August 2017