使用group_by(多个变量)时,dplyr问题 [英] dplyr issues when using group_by(multiple variables)
问题描述
我想开始使用dplyr代替ddply,但是我无法得到它的工作原理(我已经阅读了文档)。
例如,为什么当我尝试mutate()时,group_by功能不能正常工作?
查看mtcars:
库(汽车)
说我做一个data.frame这是mtcars的总结,按cyl和gear分组:
df1< - mtcars%。%
group_by(cyl,gear)%。%
总结(
newvar = sum(wt)
)
然后说我想进一步总结这个数据框。使用ddply,这很简单,但是当我尝试用dplyr时,实际上并不是分组的:
df2< - df1%。%
group_by(cyl)%。%
mutate(
newvar2 = newvar + 5
)
仍然产生未分组的输出:
cyl齿轮newvar newvar2
1 6 3 6.675 11.675
2 4 4 19.025 24.025
3 6 4 12.375 17.375
4 6 5 2.770 7.770
5 4 3 2.465 7.465
6 8 3 49.249 54.249
7 4 5 3.653 8.653
8 8 5 6.740 11.740
我做错了语法?
编辑:
如果我用plyr和ddply这样做:
df1< - ddply(mtcars, (cyl,gear),总结,newvar = sum(wt))
然后得到第二个df:
df2< - ddply(df1,。(cyl),总结,newvar2 = sum(newvar)+ 5)
但是同样的方法,sum(newvar)+ 5在summaryize()函数不适用于dplyr ...
让Dickoa的答案进一步 - 就像Hadley所说的总结剥离一个单一的分组。它从您应用它的相反顺序剥离分组,所以您可以使用
mtcars%>%
group_by(cyl,gear)%>%
总结(newvar = sum(wt))%>%
总结(newvar2 = sum(newvar)+ 5)
请注意,如果您使用 group_by(gear,cyl)
在第二行。
要让您的第一个尝试工作:
df1< - mtcars%>%
group_by(cyl,gear)%>%
总结(newvar = sum(wt))
df2 <-df1%>%
group_by(cyl)%>%
总汇(newvar2 = sum(newvar)+5)
I want to start using dplyr in place of ddply but I can't get a handle on how it works (I've read the documentation).
For example, why when I try to mutate() something does the "group_by" function not work as it's supposed to?
Looking at mtcars:
library(car)
Say I make a data.frame which is a summary of mtcars, grouped by "cyl" and "gear":
df1 <- mtcars %.%
group_by(cyl, gear) %.%
summarise(
newvar = sum(wt)
)
Then say I want to further summarise this dataframe. With ddply, it'd be straightforward, but when I try to do with with dplyr, it's not actually "grouping by":
df2 <- df1 %.%
group_by(cyl) %.%
mutate(
newvar2 = newvar + 5
)
Still yields an ungrouped output:
cyl gear newvar newvar2
1 6 3 6.675 11.675
2 4 4 19.025 24.025
3 6 4 12.375 17.375
4 6 5 2.770 7.770
5 4 3 2.465 7.465
6 8 3 49.249 54.249
7 4 5 3.653 8.653
8 8 5 6.740 11.740
Am I doing something wrong with the syntax?
Edit:
If I were to do this with plyr and ddply:
df1 <- ddply(mtcars, .(cyl, gear), summarise, newvar = sum(wt))
and then to get the second df:
df2 <- ddply(df1, .(cyl), summarise, newvar2 = sum(newvar) + 5)
But that same approach, with sum(newvar) + 5 in the summarise() function doesn't work with dplyr...
Taking Dickoa's answer one step further -- as Hadley says "summarise peels off a single layer of grouping". It peels off grouping from the reverse order in which you applied it so you can just use
mtcars %>%
group_by(cyl, gear) %>%
summarise(newvar = sum(wt)) %>%
summarise(newvar2 = sum(newvar) + 5)
Note that this will give a different answer if you use group_by(gear, cyl)
in the second line.
And to get your first attempt working:
df1 <- mtcars %>%
group_by(cyl, gear) %>%
summarise(newvar = sum(wt))
df2 <- df1 %>%
group_by(cyl) %>%
summarise(newvar2 = sum(newvar)+5)
这篇关于使用group_by(多个变量)时,dplyr问题的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!