如何在 r 中绘制两个直方图？

Question

我正在使用R，并且有两个数据框：胡萝卜和黄瓜。 每个数据框都有一个数字列，其中列出了所有测得的胡萝卜（总计：100k胡萝卜）和黄瓜（总计：50k黄瓜）的长度。 我希望在同一图上绘制两个直方图-胡萝卜长度和黄瓜长度。 它们是重叠的，所以我想我也需要一些透明度。 我还需要使用相对频率而不是绝对数字，因为每个组中的实例数量不同。 像这样的东西会很好，但是我不明白该如何从我的两个表中创建它：

转载于:https://stackoverflow.com/questions/3541713/how-to-plot-two-histograms-together-in-r

Answer 1

That image you linked to was for density curves, not histograms.

If you've been reading on ggplot then maybe the only thing you're missing is combining your two data frames into one long one.

So, let's start with something like what you have, two separate sets of data and combine them.

carrots <- data.frame(length = rnorm(100000, 6, 2))
cukes <- data.frame(length = rnorm(50000, 7, 2.5))

#Now, combine your two dataframes into one.  First make a new column in each that will be a variable to identify where they came from later.
carrots$veg <- 'carrot'
cukes$veg <- 'cuke'

#and combine into your new data frame vegLengths
vegLengths <- rbind(carrots, cukes)

After that, which is unnecessary if your data is in long formal already, you only need one line to make your plot.

ggplot(vegLengths, aes(length, fill = veg)) + geom_density(alpha = 0.2)

Now, if you really did want histograms the following will work. Note that you must change position from the default "stack" argument. You might miss that if you don't really have an idea of what your data should look like. A higher alpha looks better there. Also note that I made it density histograms. It's easy to remove the y = ..density.. to get it back to counts.

ggplot(vegLengths, aes(length, fill = veg)) + 
   geom_histogram(alpha = 0.5, aes(y = ..density..), position = 'identity')