如何在没有循环的情况下在 R 中重塑 data.frame？

Question

我在 R 中有一个 data.frame。我需要比较两行数据，如果它们相同，我需要合并行并将数据合并到一列中。我觉得这是使用 R 时的常见需求，因此使用 ddply 或其他一些包应该能够完成此任务。下面是原样的数据，dat，以及经过一些代码后它应该是什么样的，foo.我是 R 的新手，所以非常感谢任何帮助。

之前：

 dat <- structure(list(detected_id = c(11, 11, 4), reviewer_name = c("mike", 
"mike", "john"), created_at = c("2016-05-04 10:02:45", "2016-05-04 10:02:45", 
"2016-05-04 10:02:45"), stage = c(2L, 2L, 1L), V7 = c("Detected Organism: Staphylococcus Aureus, Comment: Looks good", 
"Detected Organism: Staphylococcus Aureus, Comment: Note 1", 
"Detected Organism: Human Adenovirus 7, Comment: test")), .Names = c("detected_id", 
"reviewer_name", "created_at", "stage", "V7"), row.names = c(NA, 
-3L), class = "data.frame")

之后：

foo <- structure(list(detected_id = c(11L, 4L), reviewer_name = c("mike", 
"john"), created_at = structure(c(1L, 1L), .Label = "5/4/16 10:02", class = "factor"), 
    stage = c(2L, 1L), V7 = structure(c(2L, 1L), .Label = c("Detected Organism: Human Adenovirus 7, Comment: test", 
    "Detected Organism: Staphylococcus Aureus, Comment: Looks good; Detected Organism: Staphylococcus Aureus, Comment: Note 1"
    ), class = "factor")), .Names = c("detected_id", "reviewer_name", 
"created_at", "stage", "V7"), row.names = c(NA, -2L), class = "data.frame")

编辑：

下面的解决方案适用于我提供的数据集，但我发现这些解决方案实际上并没有按预期工作。这是失败的 data.frame 示例。请注意，detected_id 列对我来说已经过时了。

dat <- structure(list(detected_id = c(11, 11, 11, 11, 12, 4), reviewer_name = c("Mike", 
"Mike", "Mike", "Mike", "John", "John"), created_at = c("2016-05-04 10:02:45", 
"2016-05-04 10:02:45", "2016-05-04 10:02:45", "2016-05-04 10:02:45", 
"2016-05-04 10:02:45", "2016-05-04 10:02:45"), stage = c(2L, 
3L, 2L, 3L, 1L, 1L), V7 = c("Detected Organism: Staphylococcus Aureus, Comment: Looks good", 
"Detected Organism: Staphylococcus Aureus, Comment: Looks good", 
"Detected Organism: Staphylococcus Aureus, Comment: Note 1", 
"Detected Organism: Staphylococcus Aureus, Comment: Note 1", 
"Detected Organism: Stenotrophomonas Maltophilia, Comment: new note", 
"Detected Organism: Human Adenovirus 7, Comment: test")), .Names = c("detected_id", 
"reviewer_name", "created_at", "stage", "V7"), row.names = c(NA, 
-6L), class = "data.frame")

解决方案：在重塑 data.frame 之前删除 detected_id 列，谢谢@eddi

Answer 1

library(data.table)

setDT(dat)[, paste(V7, collapse = "; ")
           , by = .(detected_id, reviewer_name, created_at, stage)]
#   detected_id reviewer_name          created_at stage
#1:          11          mike 2016-05-04 10:02:45     2
#2:           4          john 2016-05-04 10:02:45     1
#                                                                                                                         V1
#1: Detected Organism: Staphylococcus Aureus, Comment: Looks good; Detected Organism: Staphylococcus Aureus, Comment: Note 1
#2:                                                                     Detected Organism: Human Adenovirus 7, Comment: test

Answer 2

使用基数 R

with(dat, aggregate(V7,list(detected_id=detected_id, reviewer_name=reviewer_name, created_at=created_at, stage=stage),paste,collapse=' '))

如何在没有循环的情况下在 R 中重塑 data.frame？

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