根据R中相等的行创建新列 [英] creating new column based on rows being equal in R

问题描述

这是一个简单的问题，关于在不同列中的一个列匹配条件中以行复制为条件创建新列。具体来说，如果行在对列中是重复的，则根据y列中等于/不等的行创建新列new。

Here is a simple question about creating a new column conditional on a row duplicate in one column matching criterion in different column. Specifically, if the row is a duplicate in column "pairs", create new column "new" based on rows in column "y" being equal/unequal.

在实际数据框我对其他列有更多条件，但我的主要问题是使这些条件依赖于对列中的行相同。

In the actual data frame I have even more conditions for other columns but my main issue is with making these conditions dependent on the rows being the same in the "pairs" column.

非常感谢！

pairs y   new    

 1    1    1    
 1    0    1      
 2    1    0     
 2    1    0    
 3    3    1
 3    1    1

推荐答案

假设值始终是成对的，即每组中只有两行：

Assuming values are always paired, i.e., there are only two row in each group:

DF <- read.table(text="pairs y   new    
1    1    1    
1    0    1      
2    1    0     
2    1    0    
3    3    1
3    1    1", header=TRUE)

library(plyr)
#for integers:
ddply(DF, .(pairs), transform, new1 = 1*(diff(y) != 0L))
#for numerics:
ddply(DF, .(pairs), transform, new1 = 1*(abs(diff(y)) > .Machine$double.eps ^ 0.5))

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