R:子集增加值到最大值不包括减少 [英] R: Subsetting on increasing value to max excluding the decreasing

问题描述

我进行了多次试验，其中一个变量增加到感兴趣的最大值，然后又减少到起点.我将如何仅保留将值增加到最大值的观察结果.谢谢.

I have a number of trials where one variable increases to a max of interest then decreases back to a starting point. How would I go about just retaining the observations with the increasing values to max. Thanks.

例如

Trial A B C
    1 2 4 1
    1 4 3 2
    1 3 7 3
    1 3 3 2
    1 4 1 1
    2 4 1 1
    2 6 2 2
    2 3 1 3
    2 1 1 2
    2 7 3 1
    ...

所以我们将检查 C 上的最大值并保留如下，

So we would check max on C and retain as follows,

Trial A B C
    1 2 4 1
    1 4 3 2
    1 3 7 3
    2 4 1 1
    2 6 2 2
    2 3 1 3
    ...

最终我会有一个较低的截止值，并且可能会改变我所说的最大值的意思，但基本上以上就是目标.

Ultimately I'll have a low cut off value as well as varying perhaps what I mean by max but essentially the above is the aim.

推荐答案

可能不是最有效的解决方案，但这里尝试使用 data.table

Probably not the most efficient solution, but here is an attempt using data.table

library(data.table)
setDT(df)[, .SD[1:which.max(C)], by = Trial]
#    Trial A B C
# 1:     1 2 4 1
# 2:     1 4 3 2
# 3:     1 3 7 3
# 4:     2 4 1 1
# 5:     2 6 2 2
# 6:     2 3 1 3

或者为了提高效率

indx <- setDT(df)[, .I[1:which.max(C)], by = Trial]
df[indx$V1]

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