从 R 中的多行总结状态

Question

我想知道如何跨多行汇总特定 ID 的状态。首先，我知道如何使用 BY 语句在 SAS 中执行此操作。最后。但不确定如何在 R 中实现相同的目标。

需要汇总的数据示例， 即对于每个 ID，颜色列是：“仅红色”、“仅蓝色”或“两者”

生成数据框

example <- data.frame(id = c("A1", "A1", "A1", "A2", "A3", "A3", "A4", "A4", "A4", "A5", "A5", "A6"),
                      colour = c("red", "red", "blue", "red", "blue", "blue", "red", "red", "red", "red", "blue", "red"))

输出表

   id colour
1  A1    red
2  A1    red
3  A1   blue
4  A2    red
5  A3   blue
6  A3   blue
7  A4    red
8  A4    red
9  A4    red
10 A5    red
11 A5   blue
12 A6    red

想要的结果

  id    status
1 A1      both
2 A2  red only
3 A3 blue only
4 A4  red only
5 A5      both
6 A6  red only

SAS 中的等效代码为：

data table1 (keep=id status);
set example;
by id;
retain red_count blue_count;

if first.id then do;
  red_count = 0;
  blue_count = 0;
end;

if colour = "red" then red_count+1;
if colour = "blue" then blue_count+1;

if last.id then do;
  if red_count > 0 and blue_count > 0 then status = "both";
  else if red_count > 0  then status = "red only";
  else if blue_count > 0 then status = "blue only";
  output;
end;

run;