R：如何按行将一个sparce矩阵转换为一个列表（或事务）？

Question

我有这样的数据：

ID=c("A123","A123","A123","A123","B456","B456","B456","C789","C789")
item=c("bread", "butter", "milk", "eggs", "meat","milk", "peas", "peas", "meat")

df=data.frame(cbind(ID, item))
ID   item
1 A123  bread
2 A123 butter
3 A123   milk
4 A123   eggs
5 B456   meat
6 B456   milk
7 B456   peas
8 C789   peas
9 C789   meat

我已经变成了像这样的sparce矩阵：

df_g = dcast(df,ID~item,fill=0, length)

df_g
    ID bread butter eggs meat milk peas
1 A123     1      1    1    0    1    0
2 B456     0      0    0    1    1    1
3 C789     0      0    0    1    0    1

我怎样才能将df_g-data送到这个“篮子”形式？：

ID      basket
A123    bread,butter,eggs,milk
B456    meat,milk,peas
C789    meat,peas

我知道将df直接转换为“baskets”形式很容易。然而，这不是解决方案。将数据从df转换为df_g时，数据的顺序会发生变化，这就是为什么我需要从df_g -data获取“baskets”-form的原因。