我有一个 Dataframe df：

df=data.frame("temp"=c(60.80,46.04,26.96,24.98),"humid"=c(93.79,53.33,50.34,54.65),"wind_speed"=c(40.27,39.12,14.96, 13.81), "date" =c("2013-01-01","2013-01-03","2013-02-01", "2013-02-02"))
df$date <- as.Date(df$date, "%Y-%m-%d")
  temp   humid    wind_speed      date
1 60.80  93.79     40.27          2013-01-01
2 46.04  53.33     39.12          2013-01-03
3 26.96  50.34     14.96          2013-02-01
4 24.98  54.65     13.81          2013-02-02

我用下面这行代码将它转换为如下所示：

df_mod<- cbind(df[4], stack(df_w_delays_mod[1:3]))
  metric      values          date
  temp        60.80          2013-01-01
  temp        46.04          2013-01-03
  temp        26.96          2013-02-01
  temp        24.98          2013-02-02
  humid       93.79          2013-01-01  
  humid       53.33          2013-01-03
  humid       50.34          2013-02-01
  humid       54.65          2013-02-02
  wind_speed  40.27          2013-01-01
  wind_speed  39.12          2013-01-03
  wind_speed  14.96          2013-02-01
  wind_speed  13.81          2013-02-02

那么我已经提取了月份：

transform(df,  month = month(date, label=TRUE))
  metric      values         month
  temp        60.80          Jan
  temp        46.04          Jan
  temp        26.96          Feb
  temp        24.98          Feb
...

现在，我尝试构建一个类似的图表。

我想得到每个条形高度的平均值，所以我想按月和变量分组，然后取每个月内的平均值。
我正在尝试这个代码，但它给我错误。

df_mod %>%
group_by(metric) %>% 
  summarize(mean= mean(values)) %>% 
ggplot(aes(fill=metric, y=mean, x=month)) + 
  geom_bar(position="dodge", stat="identity") +
  theme_bw()+
  labs(title="Weather metrics", 
       x="", y = "values")
Don't know how to automatically pick scale for object of type function. Defaulting to continuous.
Error in `f()`:
! Aesthetics must be valid data columns. Problematic aesthetic(s): x = month. 
Did you mistype the name of a data column or forget to add after_stat()?
Run `rlang::last_error()` to see where the error occurred.

我还尝试过group_by（月份、公制），结果显示

`summarise()` has grouped output by '.groups'. You can override using the `.groups` argument.

有人能帮我一下吗？