R将多行折叠成1行-相同的列 [英] R collapse multiple rows into 1 row - same columns

问题描述

这是对我昨晚回答的一个问题的支持，因为我正在重新考虑如何格式化我的数据.我进行了搜索，但找不到任何适用的答案；我可能使用错误的字词进行搜索.

This is piggy backing on a question I answered last night as I am reconsidering how I'd like to format my data. I did search but couldn't find up with any applicable answer; I may be searching with wrong terms.

我有一个包含许多行的数据表，我想合并它们:

I have a data table with many rows that I'd like to combine:

record_numb <- c(1,1,1,2,2,2)
col_a <- c(123,'','',987,'','')
col_b <- c('','234','','','765','')
col_c <- c('','','543','','','543')
df <- data.frame(record_numb,col_a,col_b,col_c)
library(data.table)
setDT(df)

record_numb    col_a    col_b     col_c
1               123
1                       234
1                                 345
2               987
2                       765
2                               543

每一行将始终填充 col_a、col_b 或 col_c.它永远不会有超过这 3 个中的 1 个.我想将这些数据透视(?)到每条记录的一行，所以它看起来像这样:

Each row will always have either col_a, col_b, or col_c populated. It will never have more than 1 of those 3 populated. I'd like to pivot(?) these into a single row per record so it appears like this:

record_numb     col_a   col_b   col_c
1               123     234     345
2               987     765     543

我玩过一些 melt/cast，但我是 R 的新手，我的一半问题是知道什么是可用的.有很多东西可以使用，我希望你们中的某个人可以指出我脑海中的一个包或功能.我进行的搜索表明我要熔化和铸造等，但我无法将其应用于这种情况.我愿意使用任何功能或包.

I played with melt/cast a bit, but I'm such a novice at R that half of my issue is knowing what is available to use. There is just so much to use that I'm hoping one of you can point me to a package or function off the top of your head. My searches I performed pointed me to melt and cast and such, but I was unable to apply it to this case. I'm open to using any function or package.

推荐答案

正如您在评论中建议您希望使用 data.table 解决方案，您可以使用

As you suggested that you would like a data.table solution in your comment, you could use

library(data.table)
df <- data.table(record_numb,col_a,col_b,col_c)

df[, lapply(.SD, paste0, collapse=""), by=record_numb]
   record_numb col_a col_b col_c
1:           1   123   234   543
2:           2   987   765   543

.SD 基本上说，获取我的 data.table 中的所有变量"，除了 by 参数中的变量.在@Frank 的回答中，他使用.SDcols 减少了变量集.如果您想将变量转换为数字，您仍然可以在一行中执行此操作.这是一个链接方法.

.SD basically says, "take all the variables in my data.table" except those in the by argument. In @Frank's answer, he reduces the set of the variables using .SDcols. If you want to cast the variables into numeric, you can still do this in one line. Here is a chaining method.

df[, lapply(.SD, paste0, collapse=""), by=record_numb][, lapply(.SD, as.integer)]

第二个链"将所有变量转换为整数.

The second "chain" casts all the variables as integers.

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