Question

    @RestController 

public class ABC {

private static final Logger logger = LoggerFactory.getLogger(ABC.class);
private static volatile byte[] abc = null;
static volatile boolean xyz = "true"


// Multithreaded program where multiple threads read and write 
   both 'abc'  and 'xyz'

但是我想保留a <- c(rep("A", 3), rep("B", 3), rep("C",2)) b <- c(1,1,2,4,1,1,2,2) df <- data.frame(a,b)，b和"A"的最高"B"值。

所以我的新df只有3行。谢谢！！！

Answer 1

使用dplyr很简单：我们仅将a和summarize的值按max分组（对于每个组）：b的{{1}}值：

library(dplyr)
df %>%
    group_by(a) %>%
    summarize(b = max(b))

  a         b
  <fct> <dbl>
1 A         2
2 B         4
3 C         2

Answer 2

按a分组，最多取b

  df%>%
  group_by(a)%>%
  summarise(max(b))

过滤数据框以仅保留每个组中的最大值

2 个答案: