How to select max value FOR THE FIRST TIME of a column

Question

I have a data look like:

power = seq(1:10)
Rsq = c(-0.503268561,-0.337920056,-0.000470763,0.204181075,0.299591119,0.376839371,0.424761718, 0.424487633, 0.642269314, 0.194640766)
df = data.frame(power,Rsq)

Now, I want to choose max value FOR THE FIRST TIME in the column 'Rsq'. From that, my expected result look like:

power ------- Rsq

7 ----------0.424761718

Oh, due to my poor grasp of English skills, I don't even know this problem called a local maximum. Thanks @Reeza — Huy Nguyen, Jun 26 '20 at 19:37
If you search with the same term everyone else uses, you're more likely to find relevant answers. — Reeza, Jun 26 '20 at 19:45

akrun · Accepted Answer · 2020-06-26T19:26:24.423

1

We can get the difference of adjacent elements in 'Rsq', check if it is less than 0 and get the index of the max

library(dplyr)
df %>%
    slice(which.max(c(diff(Rsq), NA) < 0))
#   power       Rsq
#1     7 0.4247617

edited Jun 26 '20 at 19:26

answered Jun 26 '20 at 19:16

akrun

874,273
37
540
662

score 0 · Answer 2 · answered Jun 26 '20 at 19:22

0

In Base-R

  df[which.max(df$Rsq),]

  power       Rsq
7     7 0.4247617

answered Jun 26 '20 at 19:22

Daniel O

4,258
6
20

No, your solution will result in the power of 9 with Rsq of 0.642269314 . Anyway, thanks ! – Huy Nguyen Jun 26 '20 at 19:24

How to select max value FOR THE FIRST TIME of a column

2 Answers2