find the maximum value in a list of vectors in R

Question

I have a list that contains vectors of length 2, the first element of the vector denotes one data type, and the second - the second data type

[[1]]
[1] "51224.99" "0.879"   

[[2]]
[1] "51224.50" "0.038"   

[[3]]
[1] "51224.00" "0.038"   

[[4]]
[1] "51223.50" "0.038"   

[[5]]
[1] "51223.00" "0.062"   

[[6]]
[1] "51222.50" "0.038"   

[[7]]
[1] "51222.00" "0.038"   

[[8]]
[1] "51221.86" "0.370"   

[[9]]
[1] "51221.82" "0.015"   

[[10]]
[1] "51221.50" "0.038"   

[[11]]
[1] "51221.44" "2.100"   

[[12]]
[1] "51221.39" "0.196"   

[[13]]
[1] "51221.00" "0.038"   

[[14]]
[1] "51220.50" "0.038"   

[[15]]
[1] "51220.19" "0.292"   

[[16]]
[1] "51220.00" "0.038"   

[[17]]
[1] "51219.97" "0.012"   

[[18]]
[1] "51219.62" "0.684"   

[[19]]
[1] "51219.50" "0.038"   

[[20]]
[1] "51219.02" "2.311"   

I need to find the maximum value by the second element of the vector. That is, in the end result, I should get the following result:

[1] "51219.02" "2.311" 

since the maximum second number in vectors is 2.311

Answer 1

Here is an option with rbind, extract the second column, convert to numeric, find the max index to subset the list

lst1[which.max(as.numeric(do.call(rbind, lst1)[,2]))]

Answer 2

You could just turn it into a dataframe! Here's how I would do it:

(first I make an example list to mimic yours):

ex <- purrr::map(seq(12), function(i) c(rnorm(1), rnorm(1)))

Then you can use purrr to turn it into a dataframe, and filter to filter to where the second value is the max of that column:

purrr::map_df(ex, function(x) data.frame(val1 = x[1], val2 = x[2])) %>%
  dplyr::filter(val2 == max(val2))

You should be able to use this example^ by replacing ex with the name of your list.

Answer 3

Assuming your list is called yourList, you can do the follwoing:

secondValuesNumeric <- as.numeric(sapply(yourList,"[[",2))
maxIndex <- which.max(secondValuesNumeric)
result <- yourList[[maxIndex]]