R cast无法处理唯一行

问题

我有 cluster.id 对应于这些簇。身份证我有不同的 letters 在每个簇中找到(作为简化)。

我感兴趣的是,在不同的集群中通常可以找到哪些字母(我使用了下面的代码 answer )但是,我对找到每个字母的比例不感兴趣,所以我想删除重复的行(请参阅下面的代码)。

这似乎很有效(没有错误),但演员表中充满了 'NA' 和字符串,而不是所需的计数(我在下面的代码注释中进一步解释了一切)。

有什么建议可以解决这个问题吗?或者这只是在筛选唯一行后不可能实现的?

密码

test.set <- read.table(text = "
                            cluster.id   letters
                       1          4       A
                       2          4       B
                       3          4       B
                       4          3       A
                       5          3       E
                       6          3       D
                       7          3       C
                       8          2       A
                       9          2       E
                       10          1       A", header = T, stringsAsFactors = F)



# remove irrelevant clusters (clusters which only contain 1 letter)
test.set <- test.set %>% group_by( cluster.id ) %>%
  mutate(n.letters = n_distinct(letters)) %>%
  filter(n.letters > 1) %>%
  ungroup() %>%
  select( -n.letters)

test.set
#  cluster.id letters
#<int>   <chr>
#1          4       A
#2          4       B
#3          4       B
#4          3       A
#5          3       E
#6          3       D
#7          3       C
#8          2       A
#9          2       E



# I dont want duplicated rows becasue they are misleading.
# I'm only interested in which letters are found togheter in a 
# cluster not in what proportions
# Therefore I want to remove these duplicated rows

test.set.unique <- test.set %>% unique()
matrix <- acast(test.set.unique, cluster.id ~ letters)

matrix
#  A   B   C   D   E  
#2 "A" NA  NA  NA  "E"
#3 "A" NA  "C" "D" "E"
#4 "A" "B" NA  NA  NA 


# This matrix contains NA values and letters intead of the counts I wanted.
# However using the matrix before filtering for unique rows works fine

matrix <- acast(test.set, cluster.id ~ letters)
matrix
#  A B C D E
#2 1 0 0 0 1
#3 1 0 1 1 1
#4 1 2 0 0 0