R, extracting value from one attribute based on another attribute - r

Question

I've run some analysis that outputs data in the following format:
> sft
Power SFT.R.sq slope truncated.R.sq mean.k. median.k. max.k.
1 1 0.35400 8.4300 0.7710 146.00 145.00 166.0
2 2 0.21900 2.2500 0.8960 83.30 82.80 107.0
3 3 0.17300 1.1600 0.9310 49.90 49.80 72.0
4 4 0.04100 0.3070 0.7360 31.60 31.20 50.3
5 5 0.00165 -0.0298 0.4610 21.30 21.00 37.3
6 6 0.05310 -0.1780 -0.1240 15.30 14.60 28.9
7 7 0.21300 -0.2610 -0.0113 11.60 10.90 24.0
8 8 0.63800 -0.5280 0.5560 9.27 8.18 22.3
9 9 0.82500 -0.6310 0.8110 7.69 6.14 21.2
10 10 0.85000 -0.7400 0.8100 6.59 4.97 20.3
11 11 0.82200 -0.8310 0.7710 5.77 3.95 19.6
12 12 0.81900 -0.8480 0.7680 5.16 3.27 19.0
13 13 0.73300 -0.8670 0.6660 4.67 2.80 18.4
14 14 0.65300 -0.9170 0.5840 4.28 2.39 17.9
15 15 0.70200 -0.9130 0.6440 3.97 2.22 17.4
What I want is to extract the Power that gave the highest (maximum) SFT.R.sq value.
Here is the table's attributes:
>str(sft)
List of 2
$ powerEstimate: int NA
$ fitIndices :'data.frame': 15 obs. of 7 variables:
..$ Power : int [1:15] 1 2 3 4 5 6 7 8 9 10 ...
..$ SFT.R.sq : num [1:15] 0.35392 0.21883 0.17291 0.04098 0.00165 ...
..$ slope : num [1:15] 8.4267 2.2461 1.158 0.307 -0.0298 ...
..$ truncated.R.sq: num [1:15] 0.771 0.896 0.931 0.736 0.461 ...
..$ mean.k. : num [1:15] 145.8 83.3 49.9 31.6 21.3 ...
..$ median.k. : num [1:15] 145.1 82.8 49.8 31.2 21 ...
..$ max.k. : num [1:15] 165.6 107.1 72 50.3 37.3 ...
I can grab the two columns I need easily with:
sft$fitIndices$Power
sft$fitIndices$SFT.R.sq
But I can't get the actual power associated with the highest SFT.R.sq value:
>sft$fitIndices$Power[max(sft$fitIndices$SFT.R.sq)]
integer(0)
Examples of what I'm trying to do usually involve dataframes where you extract a value based on the value from another column - but it doesn't seem to work with attributes.

Answer 1

We need which.max to return the position of max value for subsetting the 'Power'
sft$fitIndices$Power[which.max(sft$fitIndices$SFT.R.sq)]
Also, if we need to slice the row, extract the data.frame element and slice
library(dplyr)
library(purrr)
pluck(sft, "fitIndices") %>%
slice_max(n = 1, order_by = "SFT.R.sq")