使用自定义名称转置/重塑答案

【问题标题】：transpose/reshape with customised names使用自定义名称转置/重塑
【发布时间】：2018-12-30 09:27:25
【问题描述】：

创建所需的样本：

require(pacman)
p_load(data.table)
DT_start <- data.table(ID = c(1,1,1,2,2,2), valueA = c("a1","a2","a3","b1","b2","b3"), valueB = c("A1","A2","A3","B1","B2","B3"))
DT_end <- data.table(ID = c(1,2)
                     , T01_valueA = c("a1","b1")
                     , T02_valueA = c("a2","b2")
                     , T03_valueA = c("a3","b3")
                     , T01_valueB = c("A1","B1")
                     , T02_valueB = c("A2","B2")
                     , T03_valueB = c("A3","B3"))
setcolorder(DT_end, c("ID","T01_valueA","T01_valueB","T02_valueA","T02_valueB","T03_valueA","T03_valueB"))

我有：

> DT_start
   ID valueA valueB
1:  1     a1     A1
2:  1     a2     A2
3:  1     a3     A3
4:  2     b1     B1
5:  2     b2     B2
6:  2     b3     B3

我需要：

> DT_end
   ID T01_valueA T01_valueB T02_valueA T02_valueB T03_valueA T03_valueB
1:  1         a1         A1         a2         A2         a3         A3
2:  2         b1         B1         b2         B2         b3         B3

如何实现呢？基本上将 DT_start 转换为 DT_end 自定义名称：T01, T02, T03...

【问题讨论】：

标签： r data.table reshape transpose

【解决方案1】：

使用末尾注释中的输入DT，我们在ID 列s 中创建一个序列，将其熔化为长格式，然后将其转换回所需的宽格式。（dcast 公式也可以写成ID ~ s + variable。）

library(data.table)

DT[, s := sprintf("T%02d", seq_along(.I)), ID]
m <- melt(DT, id.vars = c("ID", "s"))
dcast(m, ID ~ ...)

给予：

   ID T01_valueA T01_valueB T02_valueA T02_valueB T03_valueA T03_valueB
1:  1         a1         A1         a2         A2         a3         A3
2:  2         b1         B1         b2         B2         b3         B3

注意：

使用的输入：

library(data.table)

DF <- structure(list(ID = c(1L, 1L, 1L, 2L, 2L, 2L), valueA = c("a1", 
 "a2", "a3", "b1", "b2", "b3"), valueB = c("A1", "A2", "A3", "B1", 
 "B2", "B3")), class = "data.frame", 
 row.names = c(NA, -6L))
DT <- as.data.table(DF)

【讨论】：