通常在我們寫論文時，所需要的統(tǒng)計圖是非常嚴(yán)謹(jǐn)?shù)模锩娴南ＥD字符與上下腳標(biāo)都必須要嚴(yán)格書寫。因此在使用R繪圖時，如何在我們目標(biāo)圖中使用希臘字符、上標(biāo)、下標(biāo)及一些數(shù)學(xué)公式呢？在本博客中我們會進(jìn)行詳細(xì)的說明。

后面我們都將以一個最簡單的繪圖為例，只是將其標(biāo)題進(jìn)行修改。

希臘字母

使用希臘字符、上標(biāo)、下標(biāo)及數(shù)學(xué)公式，都需要利用一個函數(shù)：expression()，具體使用方式如下：

plot(cars)
title(main = expression(Sigma))

輸出：

上下標(biāo)

expression()中的下標(biāo)為[]，上標(biāo)為^，空格為~，連接符為*。示例代碼如下：

plot(cars)
title(main = expression(Sigma[1]~'a'*'n'*'d'~Sigma^2))

輸出：

paste

想達(dá)到上面的效果，我們其實(shí)可以使用paste()與expression()進(jìn)行組合，不需要上述繁瑣的過程，也能夠達(dá)到我們上述一模一樣的輸出，并且方便快捷：

plot(cars)
title(main = expression(paste(Sigma[1], ' and ', Sigma^2)))

一個復(fù)雜的例子

目標(biāo)：

代碼：

expression(paste((frac(1, m)+frac(1, n))^-1, ABCD[paste(m, ',', n)]))

進(jìn)階

在我們想批量產(chǎn)生大量含有不同變量值的標(biāo)題時，如果遇到變量與公式的混合輸出該如何操作，

可參考前文：R語言繪圖公式與變量對象混合拼接實(shí)現(xiàn)方法

數(shù)學(xué)公式

最后的數(shù)學(xué)公式，只需要在expression()中進(jìn)行相應(yīng)的符號連接即可

具體要求可參考：Mathematical Annotation in R

鑒于其很不穩(wěn)定，這里將里面的細(xì)節(jié)搬運(yùn)過來。

（下表也可以直接在 R help 中搜索 plotmath 獲取。）

Syntax	Meaning
x + y	x plus y
x - y	x minus y
x*y	juxtapose x and y
x/y	x forwardslash y
x %±% y	x plus or minus y
x %/% y	x divided by y
x %*% y	x times y
x %.% y	x cdot y
x[i]	x subscript i
x^2	x superscript 2
paste(x, y, z)	juxtapose x, y, and z
sqrt(x)	square root of x
sqrt(x, y)	yth root of x
x == y	x equals y
x != y	x is not equal to y
x < y	x is less than y
x <= y	x is less than or equal to y
x > y	x is greater than y
x >= y	x is greater than or equal to y
!x	not x
x %~~% y	x is approximately equal to y
x %=~% y	x and y are congruent
x %==% y	x is defined as y
x %prop% y	x is proportional to y
x %~% y	x is distributed as y
plain(x)	draw x in normal font
bold(x)	draw x in bold font
italic(x)	draw x in italic font
bolditalic(x)	draw x in bolditalic font
symbol(x)	draw x in symbol font
list(x, y, z)	comma-separated list
…	ellipsis (height varies)
cdots	ellipsis (vertically centred)
ldots	ellipsis (at baseline)
x %subset% y	x is a proper subset of y
x %subseteq% y	x is a subset of y
x %notsubset% y	x is not a subset of y
x %supset% y	x is a proper superset of y
x %supseteq% y	x is a superset of y
x %in% y	x is an element of y
x %notin% y	x is not an element of y
hat(x)	x with a circumflex
tilde(x)	x with a tilde
dot(x)	x with a dot
ring(x)	x with a ring
bar(xy)	xy with bar
widehat(xy)	xy with a wide circumflex
widetilde(xy)	xy with a wide tilde
x %<->% y	x double-arrow y
x %->% y	x right-arrow y
x %<-% y	x left-arrow y
x %up% y	x up-arrow y
x %down% y	x down-arrow y
x %<=>% y	x is equivalent to y
x %=>% y	x implies y
x %<=% y	y implies x
x %dblup% y	x double-up-arrow y
x %dbldown% y	x double-down-arrow y
alpha – omega	Greek symbols
Alpha – Omega	uppercase Greek symbols
theta1, phi1, sigma1, omega1	cursive Greek symbols
Upsilon1	capital upsilon with hook
aleph	first letter of Hebrew alphabet
infinity	infinity symbol
partialdiff	partial differential symbol
nabla	nabla, gradient symbol
32*degree	32 degrees
60*minute	60 minutes of angle
30*second	30 seconds of angle
displaystyle(x)	draw x in normal size (extra spacing)
textstyle(x)	draw x in normal size
scriptstyle(x)	draw x in small size
scriptscriptstyle(x)	draw x in very small size
underline(x)	draw x underlined
x ~~ y	put extra space between x and y
x + phantom(0) + y	leave gap for “0”, but don't draw it
x + over(1, phantom(0))	leave vertical gap for “0” (don't draw)
frac(x, y)	x over y
over(x, y)	x over y
atop(x, y)	x over y (no horizontal bar)
sum(x[i], i==1, n)	sum x[i] for i equals 1 to n
prod(plain§(X==x), x)	product of P(X=x) for all values of x
integral(f(x)*dx, a, b)	definite integral of f(x) wrt x
union(A[i], i==1, n)	union of A[i] for i equals 1 to n
intersect(A[i], i==1, n)	intersection of A[i]
lim(f(x), x %->% 0)	limit of f(x) as x tends to 0
min(g(x), x > 0)	minimum of g(x) for x greater than 0
inf(S)	infimum of S
sup(S)	supremum of S
x^y + z	normal operator precedence
x^(y + z)	visible grouping of operands
x^{y + z}	invisible grouping of operands
group("(",list(a, b),"]")	specify left and right delimiters
bgroup("(",atop(x,y),")")	use scalable delimiters
group(lceil, x, rceil)	special delimiters
group(lfloor, x, rfloor)	special delimiters