计数在数据表中由2列唯一 [英] count unique by 2 columns in a data table
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问题描述
我在r中有一个data.table
I have a data.table in r
col1 col2 col3 col4
1: 5.1 3.5 1.4 setosa
2: 5.1 3.5 1.4 setosa
3: 4.7 3.2 1.3 setosa
4: 4.6 3.1 1.5 setosa
5: 5.0 3.6 1.4 setosa
6: 5.1 3.5 3.4 eer
7: 5.1 3.5 3.4 eer
8: 5.1 3.2 1.3 eer
9: 5.1 3.5 1.5 eer
10: 5.1 3.5 1.4 eer
DT <- structure(list(col1 = c(5.1, 5.1, 4.7, 4.6, 5, 5.1, 5.1, 5.1,
5.1, 5.1), col2 = c(3.5, 3.5, 3.2, 3.1, 3.6, 3.5, 3.5, 3.2, 3.5,
3.5), col3 = c(1.4, 1.4, 1.3, 1.5, 1.4, 3.4, 3.4, 1.3, 1.5, 1.4
), col4 = structure(c(1L, 1L, 1L, 1L, 1L, 4L, 4L, 4L, 4L, 4L), .Label = c("setosa",
"versicolor", "virginica", "eer"), class = "factor")), .Names = c("col1",
"col2", "col3", "col4"), row.names = c(NA, -10L), class = c("data.table",
"data.frame"))
col4
的每个值的 col1
和 col2
预期输出为
col1 col2 col3 col4 count
1: 5.1 3.5 1.4 setosa 4
2: 5.1 3.5 1.4 setosa 4
3: 4.7 3.2 1.3 setosa 4
4: 4.6 3.1 1.5 setosa 4
5: 5.0 3.6 1.4 setosa 4
6: 5.1 3.5 3.4 eer 2
7: 5.1 3.5 3.4 eer 2
8: 5.1 3.2 1.3 eer 2
9: 5.1 3.5 1.5 eer 2
10: 5.1 3.5 1.4 eer 2
如何在1 data.table语法中这样做? / p>
How can I do this in 1 data.table syntax only?
推荐答案
我必须先经过几次尝试,然后结束。有什么好的吗?
I had to go through a few attempts first, and ended up with this. Any good?
DT[, count:=nrow(unique(.SD)), by=col4, .SDcols=c("col1","col2")]
DT
col1 col2 col3 col4 count
1: 5.1 3.5 1.4 setosa 4
2: 5.1 3.5 1.4 setosa 4
3: 4.7 3.2 1.3 setosa 4
4: 4.6 3.1 1.5 setosa 4
5: 5.0 3.6 1.4 setosa 4
6: 5.1 3.5 3.4 eer 2
7: 5.1 3.5 3.4 eer 2
8: 5.1 3.2 1.3 eer 2
9: 5.1 3.5 1.5 eer 2
10: 5.1 3.5 1.4 eer 2
>
并且相同但更快感谢下面的Procrastinatus注释:
and the same but faster thanks to Procrastinatus comment below :
DT[, count:=uniqueN(.SD), by=col4, .SDcols=c("col1","col2")]
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