如何将data.table与循环

时间：2016-11-24 09:57:12

标签： r data.table

我的数据框如下所示：

> data <- data.frame(A=c(1,1,1,2,2,3,3,3,3,3), B=c("1A","1B","1C","2A","2B","3A","3B","3C","3D","3E"))

我想添加一个在变量A和B的函数中标记的新变量。结果必须是：

  > data
   A  B LABEL
1  1 1A   1-2
2  1 1B   2-3
3  1 1C   3-4
4  2 2A   1-2
5  2 2B   2-3
6  3 3A   1-2
7  3 3B   2-3
8  3 3C   3-4
9  3 3D   4-5
10 3 3E   5-6

我尝试使用data.table函数。我尝试的代码：

> setDT(data)
> data <- data[,list(LABEL = for(i in 1:length(A)){paste(i, "-", i+1, sep="")}),by=c("A","B")]

消息错误：[.data.table中的错误（数据,,列表（LABEL = for（i in 1：length（A））{：   第一组的j结果的第1列为NULL。我们依赖第一个结果的列类型来确定剩余组的预期类型（并要求一致性）。对于以后的组，可以接受NULL列（并且这些列被替换为适当类型的NA并且被回收）但不适用于第一组。请使用类型化的空向量，例如integer（）或numeric（）。“

3 个答案:

答案 0 :(得分：3)

我们可以使用shift来创建＆＃39;引导＆＃39;将＆＃39; A＆＃39;和paste分组后的序列值与行序列一起创建＆＃39; LABEL＆＃39; 

library(data.table)
setDT(data)[, LABEL := paste(seq_len(.N), shift(seq_len(.N),
                          type='lead', fill= .N+1), sep="-"), by = A]

或者

setDT(data)[, LABEL := paste(seq_len(.N), seq_len(.N)+1, sep = "-"), by = A]
data
#    A  B LABEL
# 1: 1 1A   1-2
# 2: 1 1B   2-3
# 3: 1 1C   3-4
# 4: 2 2A   1-2
# 5: 2 2B   2-3
# 6: 3 3A   1-2
# 7: 3 3B   2-3
# 8: 3 3C   3-4
# 9: 3 3D   4-5
#10: 3 3E   5-6

或者我们可以使用base R方法

i1 <- sequence(tabulate(data$A))
data$LABEL <- paste(i1, i1+1, sep="-")
data$LABEL
#[1] "1-2" "2-3" "3-4" "1-2" "2-3" "1-2" "2-3" "3-4" "4-5" "5-6"

答案 1 :(得分：3)

您也可以使用dplyr :: mutate 

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在此按A分组，找到组中的序列并连接序列+ 1 

library(dplyr)
data %>% 
        group_by(A) %>% 
        mutate(LABEL=paste(seq_along(A),seq_along(A)+1,sep="-"))

答案 2 :(得分：3)

另一种选择是使用base R ave函数

data$LABEL <- ave(data$A, data$A, FUN = function(x) 
                                      paste0(seq_along(x), "-", seq_along(x)+1))
data
#   A  B LABEL 
#1  1 1A   1-2
#2  1 1B   2-3
#3  1 1C   3-4
#4  2 2A   1-2
#5  2 2B   2-3
#6  3 3A   1-2
#7  3 3B   2-3
#8  3 3C   3-4
#9  3 3D   4-5
#10 3 3E   5-6
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