计算r中的独特因素

Question

我想知道在记录的每个出生日期分娩的独特水坝的数量.我的数据框与此类似:

dam <- c("2A11","2A11","2A12","2A12","2A12","4D23","4D23","1X23")
bdate <- c("2009-10-01","2009-10-01","2009-10-01","2009-10-01",
           "2009-10-01","2009-10-03","2009-10-03","2009-10-03")
mydf <- data.frame(dam,bdate)
mydf
#    dam      bdate
# 1 2A11 2009-10-01
# 2 2A11 2009-10-01
# 3 2A12 2009-10-01
# 4 2A12 2009-10-01
# 5 2A12 2009-10-01
# 6 4D23 2009-10-03
# 7 4D23 2009-10-03
# 8 1X23 2009-10-03

我曾经使用aggregate(dam ~ bdate, data=mydf, FUN=length)但它计算了在特定日期生下的所有水坝

bdate dam
1 2009-10-01   5
2 2009-10-03   3

相反,我需要这样的东西:

mydf2
  bdate      dam
1 2009-10-01  2
2 2009-10-03  2

非常感激您的帮忙!

Answer 1

关于什么:

aggregate(dam ~ bdate, data=mydf, FUN=function(x) length(unique(x)))

Answer 2

您也可以先运行unique数据：

aggregate(dam ~ bdate, data=unique(mydf[c("dam","date")]), FUN=length)

然后你也可以使用table而不是aggregate，虽然输出有点不同。

> table(unique(mydf[c("dam","date")])$bdate)

2009-10-01 2009-10-03 
         2          2