我想编写一个函数，它接受一个数据帧，并将该数据帧中的所有列绘制为直方图.

I want to write a function that takes a dataframe, and graphs all the columns in that dataframe as histograms.

对于我事先知道其列名的数据框，我可以写

For a dataframe whose column names I know beforehand, I can write

qplot(colname1, data=df, geom='histogram')
qplot(colname2, data=df, geom='histogram')
...

但我想一般地这样做，以便我可以将列的名称用作字符串 "colname1".

but I want to do this generically, so that I can use the name of the column as a string "colname1".

也就是说，怎么写

plot_histogram_of_column <- function(df, colname) {
    # qplot(colname, data=df, geom='histogram') won't work
}

推荐答案

使用 ggplot 和 aes_string.像这样的:

Use ggplot and aes_string. Something like this:

ggplot(data = df, aes_string(x = colname)) + geom_histogram()

aes_string 正是为此目的而编写的.

aes_string was written precisely for this purpose.