如何以编程方式更改传递给"fill“的列名？

Question

我需要绘制一个区域堆栈图，其中的填充可以通过更改"string holder“变量以编程方式进行更改。下面是我想做的一个例子。

this_group_label <- "Roots & Tubers"
#[...lots of code in which a data frame df_plot is created with a column named "Roots & Tubers...]"
gg <- ggplot(df_plot, aes(x = year, y = `Pctge CC`, fill = this_group_label))
gg <- gg + geom_area(position = "stack")
gg

这样我就可以在处理具有不同列名的新数据框时更改存储在this_group_label中的字符串。

我已经试过aes_string()了

this_group_label <- "Roots & Tubers"
#[...lots of code in which a data frame df_plot is created with a column named "Roots & Tubers...]"
gg <- ggplot(df_plot, aes_string("year", "`Pctge CC`", fill = this_group_label))
gg <- gg + geom_area(position = "stack")
gg

和get()

this_group_label <- "Roots & Tubers"
#[...lots of code in which a data frame df_plot is created with a column named "Roots & Tubers...]"
gg <- ggplot(df_plot, aes(x = year, y = `Pctge CC`, fill = get(this_group_label)))
gg <- gg + geom_area(position = "stack")
gg

无济于事。当我尝试最后两个时，我得到了错误Error in FUN(X[[i]], ...) : object 'Roots' not found

Answer 1

这是可行的：

this_group_label <- "Roots & Tubers"
#[...lots of code in which a data frame df_plot is created with a column named "Roots & Tubers...]"
fill_label <- paste0("`", this_group_label, "`")
gg <- ggplot(df_plot, aes_string("year", "`Pctge CC`", fill = fill_label))
gg <- gg + geom_area(position = "stack")
gg

请注意，Pctge CC周围的反引号也是正常工作所必需的。

Answer 2

rlang::sym接受字符串并将其转换为符号。您只需要使用!!对其进行unquote，因为aes需要未计算的表达式：

library(rlang)

gg <- ggplot( df_plot, aes(x=year, y=`Pctge CC`, fill = !!sym(this_group_label)) )
gg <- gg + geom_area(position = "stack")
gg