通常在我們寫論文時，所需要的統計圖是非常嚴謹的，里面的希臘字符與上下腳標都必須要嚴格書寫。因此在使用R繪圖時，如何在我們目標圖中使用希臘字符、上標、下標及一些數學公式呢？在本博客中我們會進行詳細的說明。
后面我們都將以一個最簡單的繪圖為例，只是將其標題進行修改。
希臘字母
使用希臘字符、上標、下標及數學公式，都需要利用一個函數：expression()，具體使用方式如下：
plot(cars) title(main = expression(Sigma))
輸出：
上下標
expression()中的下標為[]，上標為^，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
想達到上面的效果，我們其實可以使用paste()與expression()進行組合，不需要上述繁瑣的過程，也能夠達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)))
一個復雜的例子
目標：
代碼：
expression(paste((frac(1, m)+frac(1, n))^-1, ABCD[paste(m, ',', n)]))
進階
在我們想批量產生大量含有不同變量值的標題時，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現方法
數學公式
最后的數學公式，只需要在expression()中進行相應的符號連接即可
具體要求可參考：Mathematical Annotation in R
鑒于其很不穩定，這里將里面的細節搬運過來。
（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 C omega | Greek symbols |
| Alpha C 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 |
以上就是R語言繪圖時輸出希臘字符上下標及數學公式實現方法的詳細內容，更多關于R語言繪圖輸出希臘字符上下標及數學公式的資料請關注服務器之家其它相關文章！
原文鏈接：https://blog.csdn.net/weixin_41929524/article/details/88577902
