r - Dynamically create expression for ggplot legend? -

i want plot line graph, multiple lines, coloured depending on grouping variable. want set legend labels via scale-command:

scale_color_manual(values = colors_values, labels = ...) 

the legend labels following: "x^2", "x^3", "x^4" etc., range dynamically created. dynamically create expression label text, i.e.

• "x^2" should become x²
• "x^3" should become x³

etc.

the amount of legend labels varies, thought as.expression(sprintf("x^%i", number)), of course not work label parameter scale function.

i have searched google , stack overflow, however, haven't found working solution yet, hope can me here.

here's reproducible example:

poly.term <- runif(100, 1, 60) resp <- rnorm(100, 40, 5) poly.degree <- 2:4 geom.colors <- scales::brewer_pal(palette = "set1")(length(poly.degree)) plot.df <- data.frame() (i in poly.degree) {   mydat <- na.omit(data.frame(x = poly.term, y = resp))   fit <- lm(mydat$y ~ poly(mydat$x, i, raw = true))   plot.df <- rbind(plot.df, cbind(mydat, predict(fit), sprintf("x^%i", i))) } colnames(plot.df) <- c("x","y", "pred", "grp") ggplot(plot.df, aes(x, y, colour = grp)) +   stat_smooth(method = "loess", se = f) +   geom_line(aes(y = pred))   scale_color_manual(values = geom.colors                      # here want change legend labels                      # lables = expresion???                      ) 

i have legend labels x², x³ , x⁴.

ggplot(plot.df, aes(x, y, colour = grp)) +   stat_smooth(method = "loess", se = f) +   geom_line(aes(y = pred)) +   scale_color_manual(values = setnames(geom.colors,                                        paste0("x^",poly.degree)),                      labels = setnames(lapply(poly.degree, function(i) bquote(x^.(i))),                                         paste0("x^",poly.degree))) 

it's important ensure correct mapping if change values or labels in scale. thus, should use named vectors.