R 获取数据集的一半值

我提前道歉这是我的第一篇帖子

我有以下数据集。我想获得船只达到其最大速度一半的时间（例如船只1 6秒，船只2 4秒）。我有20种不同的船只来获得其半速时间值。非常感谢

vessel  time    speed 
vessel1 1   6
vessel1 2   7
vessel1 3   10
vessel1 4   16
vessel1 5   18
vessel1 6   20
vessel1 7   22
vessel1 8   24
vessel1 9   36
vessel1 10  37
vessel1 11  38
vessel1 12  38
vessel1 13  39
vessel1 14  40
vessel1 15  41
vessel1 16  41
vessel1 17  41
vessel2 1   7
vessel2 2   9
vessel2 3   12
vessel2 4   15
vessel2 5   20
vessel2 6   22
vessel2 7   23
vessel2 8   24
vessel2 9   25
vessel2 10  26
vessel2 11  27
vessel3 12  28
vessel4 13  29
vessel5 14  30

---

应使用以下代码（将read.table替换为read.csv（“youfilename.csv”）：

mydf=max（x[，3]）/2,2]））

第一行读取数据

第二行只是为方便起见给他们起了标准化的名字

第三行通过每个船只的data.frame，找到机器超过半速的第一个时间点（即>=max（speed）/2）。

您可以执行以下操作：

d <- read.table(header=TRUE, text=
"vessel  time    speed 
vessel1 1   6
vessel1 2   7
vessel1 3   10
vessel1 4   16
vessel1 5   18
vessel1 6   20
vessel1 7   22
vessel1 8   24
vessel1 9   36
vessel1 10  37
vessel1 11  38
vessel1 12  38
vessel1 13  39
vessel1 14  40
vessel1 15  41
vessel1 16  41
vessel1 17  41
vessel2 1   7
vessel2 2   9
vessel2 3   12
vessel2 4   15
vessel2 5   20
vessel2 6   22
vessel2 7   23
vessel2 8   24
vessel2 9   25
vessel2 10  26
vessel2 11  27
vessel3 12  28
vessel4 13  29
vessel5 14  30")

which.halfspeed <- function(speed) {
  half <- max(speed)/2
  sum(speed<=half)
}

index <- tapply(d$speed, d$vessel, which.halfspeed)
index
mapply('[', split(d$time, d$vessel), index)

d获取示例数据：

df <- read.table(text="
vessel  time    speed 
vessel1 1   6
vessel1 2   7
vessel1 3   10
vessel1 4   16
vessel1 5   18
vessel1 6   20
vessel1 7   22
vessel1 8   24
vessel1 9   36
vessel1 10  37
vessel1 11  38
vessel1 12  38
vessel1 13  39
vessel1 14  40
vessel1 15  41
vessel1 16  41
vessel1 17  41
vessel2 1   7
vessel2 2   9
vessel2 3   12
vessel2 4   15
vessel2 5   20
vessel2 6   22
vessel2 7   23
vessel2 8   24
vessel2 9   25
vessel2 10  26
vessel2 11  27
vessel3 12  28
vessel4 13  29
vessel5 14  30"
,header = T)

我认为如果你调整你的问题，你将能够更有效地得到帮助。你试图用什么方法来解决这个问题？您的数据是如何存储的。。。它已经在数据帧或向量中，还是仍然在CSV中？这两个数字代表什么？数据存储在csv中。时间以秒为单位，速度以英里/小时为单位。我正在尝试获取每辆车达到其最大速度一半时的秒数。如果只有船只入口（例如vessel3），请编辑您的问题！明亮的非常感谢！多好的解决方案啊！非常感谢。
df <- read.table(text="
vessel  time    speed 
vessel1 1   6
vessel1 2   7
vessel1 3   10
vessel1 4   16
vessel1 5   18
vessel1 6   20
vessel1 7   22
vessel1 8   24
vessel1 9   36
vessel1 10  37
vessel1 11  38
vessel1 12  38
vessel1 13  39
vessel1 14  40
vessel1 15  41
vessel1 16  41
vessel1 17  41
vessel2 1   7
vessel2 2   9
vessel2 3   12
vessel2 4   15
vessel2 5   20
vessel2 6   22
vessel2 7   23
vessel2 8   24
vessel2 9   25
vessel2 10  26
vessel2 11  27
vessel3 12  28
vessel4 13  29
vessel5 14  30"
,header = T)

library(dplyr)

df %>%
  group_by(vessel) %>%              # for each vessel
  filter(speed >= max(speed)/2) %>% # keep all speed values above or equal to the half of max speed
  filter(speed == min(speed)) %>%   # keep the minimum speed value
  ungroup()                         # forget the grouping

# # A tibble: 5 x 3
#    vessel  time speed
#    <fctr> <int> <int>
# 1 vessel1     7    22
# 2 vessel2     4    15
# 3 vessel3    12    28
# 4 vessel4    13    29
# 5 vessel5    14    30