替換爲「NA」重複變量用awk

Question

假設我有一個文件：

1 Blue 
2 Red 
3 Yellow 
4 Yellow 
5 Yellow 
6 Purple 
7 Purple 
8 Green 

而且我想獲得以下文件，通過「NA」

1 Blue 
2 Red 
3 Yellow 
4 NA 
5 NA 
6 Purple 
7 NA 
8 Green 

Answer 1

代替重複的變量

試試這個 -

$ awk 'a[$2]++{$2="NA"} 1' f 
1 Blue 
2 Red 
3 Yellow 
4 NA 
5 NA 
6 Purple 
7 NA 
8 Green 

Answer 2

awk '{ if ($2 == COLOR) {print $1, "NA"} else {COLOR=$2; print $1, $2 } }' 

Answer 3

$ awk '{print $1, ($2==p ? "NA" : $2); p=$2}' file 
1 Blue 
2 Red 
3 Yellow 
4 NA 
5 NA 
6 Purple 
7 NA 
8 Green