因子水平的所有组合的综合值，包括缺失的因子

Question

我试图找到基于多列的数据帧的最小值。我能够使用下面的聚合函数成功地完成此操作。但是，结果不包含输入数据框中没有数据的因素组合。

我已经有了：

# all possibilities of fruits, cities, and vegetables: 
fruits<-c('apple','banana','grape') 
cities<-c('new york','chicago','los angeles') 
vegetables<-c('cucumber','mushroom') 

#my input (ie, a sample from a test: 
inputdf<-data.frame(fruit=c('apple','apple','apple','banana','banana','banana','grape','grape','grape'),city=c('new york','new york','new york','new york','chicago','los angeles','chicago','chicago','chicago'),vegetable=c('cucumber','cucumber','mushroom','cucumber','mushroom','mushroom','cucumber','cucumber','cucumber'),value=c(5,3,4,6,5,7,2,7,4)) 

#my aggregation: 
outdf<-aggregate(value ~ fruit + city + vegetable,inputdf,function(x) min(x)) 

我得到的输出是：

fruit city  vegetable value 
grape chicago  cucumber 2 
apple new york cucumber 3 
banana new york cucumber 6 
banana chicago  mushroom 5 
banana los angeles mushroom 7 
apple new york mushroom 4 

这是正确的，但是，我也想对应的列是didnt组合的行在输入df存在：

fruit city  vegetable value 
apple new york cucumber 3 
apple new york mushroom 4 
apple chicago  cucumber NA 
apple chicago  mushroom NA 
apple los angeles cucumber NA 
apple los angeles mushroom NA 
banana new york cucumber 6 
banana new york mushroom NA 
banana chicago  cucumber NA 
banana chicago  mushroom 5 
banana los angeles cucumber NA 
banana los angeles mushroom 7 
grape new york cucumber NA 
grape new york mushroom NA 
grape chicago  cucumber 2 
grape chicago  mushroom NA 
grape los angeles cucumber NA 
grape los angeles mushroom NA 

我希望能够做到这一点的任何数量的列上，其中吨o结合。有没有简单的方法来做到这一点？我想要输出的原因是因为我需要将NA转换为特定值并再次在相同子集上平均这些值。谢谢！

Answer 1

可以使用expand.grid生成所有组合，然后利用merge：

outdf<-aggregate(value ~ fruit + city + vegetable,inputdf,function(x) min(x)) 
DF=expand.grid(fruits, cities, vegetables) 
outdf=merge(outdf,DF,by.x=c('fruit','city','vegetable'),by.y=c('Var1','Var2','Var3'),all.y=T) 
> outdf 
    fruit  city vegetable value 
1 apple  chicago cucumber NA 
2 apple  chicago mushroom NA 
3 apple los angeles cucumber NA 
4 apple los angeles mushroom NA 
5 apple new york cucumber  3 
6 apple new york mushroom  4 
7 banana  chicago cucumber NA 
8 banana  chicago mushroom  5 
9 banana los angeles cucumber NA 
10 banana los angeles mushroom  7 
11 banana new york cucumber  6 
12 banana new york mushroom NA 
13 grape  chicago cucumber  2 
14 grape  chicago mushroom NA 
15 grape los angeles cucumber NA 
16 grape los angeles mushroom NA 
17 grape new york cucumber NA 
18 grape new york mushroom NA