比较两个表并根据条件添加行 [英] Compare two table and adding row based on condition

问题描述

我想将 dt1 与 dt2 进行比较，使得如果 dt1 与 dt2 比较的列值存在，它不会添加行或更改该行中的值.因此，当值不同时(如示例中所示)，其中 dt2 具有"4"& A列中的"5"将添加"4"& "5"到 dem1 表，但不会替换 dem1 中的"1"，"2"或"3"值列，因为它已经存在.

I would like to compare dt1 to dt2 such that if dt1 A column value exist when it compare to dt2 A column value it would not add a row or change the value in that row. So when the value are different like shown in the example where dt2 has "4" & "5" in A column it will add "4" & "5" to dt1 table but it would not replace it's "1", "2" or "3" value in dt1 A column since it existed already.

我想以主键的形式使用A列来检查以下内容:如果两个表的A列中都存在"1"，则没有任何变化，但是如果存在A列值在 dt2 (例如:"4")中，但不在 dt1 中，那么我希望合并那一行数据与dt1表

I would like to use A column in a form of a primary key to check something along the line of if "1" exist in A column in both both table then nothing changes but if in there is a A column value in dt2(Example:"4") but not in dt1 then i wan that row of data to merge with dt1 table

dt1 
A   B   C   
1   4   7   
2   5   8   
3   6   9   

dt2
A   B   C  
1   10  13  
2   12  15  
3   11  14  
4   1   20
5   12  3

dt1
A   B   C   
1   4   7   
2   5   8   
3   6   9    
4   1   20
5   12  3

推荐答案

您可以将dt1绑定到dt2中没有A值的dt2行中，只需一个条件语句

You can bind dt1 with rows from dt2 that don't have A values in dt1 with just one conditional statement

rbind(dt1, dt2[!(dt2$A %in% dt1$A),])
#   A  B  C
# 1 1  4  7
# 2 2  5  8
# 3 3  6  9
# 4 4  1 20
# 5 5 12  3

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