问题描述
我想在 ggplot2 绘图的 PHP Warning: PHP Startup: Unable to create temporary file,Check permissions in temporary files directory. in UnkNown on line 0
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层中使用下标和数字。该数字将来自索引数据帧，以便我可以在自定义函数中以灵活的方式使用它，但这里有一个更简单的可重现示例：
geom_text()挑战在于以适用于下标和格式化数字的方式使用 temp_line <- structure(list(x = c(670.892544634835,670.94367492675,670.994805218665,671.04593551058,671.097065802495,671.14819609441,671.199326386325,671.25045667824,671.301586970155,671.35271726207,671.403847553985,671.4549778459,671.506108137815,671.55723842973,671.608368721645,671.65949901356,671.710629305475,671.76175959739,671.812889889305,671.86402018122,671.915150473135,671.96628076505,672.017411056965,672.06854134888,672.119671640795,672.17080193271,672.221932224625,672.27306251654,672.324192808455,672.37532310037,672.426453392285,672.4775836842,672.528713976115,672.57984426803,672.630974559945,672.68210485186),y = c(0.985240554809607,0.982213133032921,0.986693753084667,0.987366974516756,0.987636649598203,0.982056033377924,0.980484643703154,0.983029322815495,0.988833379596215,0.983723421126925,0.984861430761356,0.975375941059582,0.973793277004997,0.974896425651856,0.976215113076567,0.980190883847887,0.97234555785344,0.976564419204803,0.971411825270084,0.958092987035761,0.948933680537213,0.944433555718954,0.955207036644352,0.966236032356096,0.97461001903587,0.982502838158965,0.977806030386617,0.980102357820749,0.971970360584438,0.972510182292617,0.971868273995148,0.986332867356837,0.992939055558675,1,0.990384208442822,0.987140151281311)),class = "data.frame",row.names = c(NA,-36L))
temp <- structure(list(x = 671.96628076505,y = 0.943555524955473),row.names = "window_mins")
temp_num <- c(window_mins = 0.000878030763480352)
# Attempt at plotting equation using paste()
ggplot() +
geom_line(data = temp_line,aes(x = x,y = y),alpha = 0.85,size = 0.6) +
geom_point(data = temp,size = 1.5,shape = 15) +
geom_text(data = temp,label = paste("L1 - L[tot] = ",formatC(temp_num,format = "e",digits = 3)),nudge_x = -0.45,show.legend = FALSE)
。我尝试将 paste() 和 expression() 一起使用。这将创建正确的下标，但不幸的是打印了 paste() 的命令和参数，而不是计算以生成数字：
formatC()我尝试了上述方法，但将 label = expression(paste("L1 - ",L[tot],"= ",digits = 3)))
命令包装在 formatC 中，但我无法使其正常工作。我还根据以下链接将整个表达式包装在 eval() 和 parse() 中。在 substitute() 命令中生成下标和格式化数字时我缺少什么？
我看过的相关帖子： Combining paste() and expression() functions in plot labels
https://community.rstudio.com/t/use-bquote-in-ggplot2-for-subscript-text/40882
R - how to combine expression(),paste() and formatC() commands for one legend element?
解决方法
好吧，这出奇地棘手。
首先，你需要学习help("plotmath")。然后，我会传递一个字符串并让 ggplot2 解析它。如果我们这样做，方程的 RHS 应指定为字符串，否则将在 plotmath 中应用标准打印格式。为方便起见，我更喜欢 sprintf，但如果您坚持可以使用 paste 和 formatC 的组合构造相同的字符串。
#note the single quotes within the string
sprintf("L1 - L[tot] == '%.3e'",temp_num)
#[1] "L1 - L[tot] == '8.780e-04'"
ggplot() +
geom_line(data = temp_line,aes(x = x,y = y),alpha = 0.85,size = 0.6) +
geom_point(data = temp,size = 1.5,shape = 15) +
geom_text(data = temp,label = sprintf("L1 - L[tot] == '%.3e'",temp_num),nudge_x = -0.45,show.legend = FALSE,parse = TRUE)
