max - How to find the highest value of a column in a data frame in R?

Question

I have the following data frame which I called ozone:

   Ozone Solar.R Wind Temp Month Day
1     41     190  7.4   67     5   1
2     36     118  8.0   72     5   2
3     12     149 12.6   74     5   3
4     18     313 11.5   62     5   4
5     NA      NA 14.3   56     5   5
6     28      NA 14.9   66     5   6
7     23     299  8.6   65     5   7
8     19      99 13.8   59     5   8
9      8      19 20.1   61     5   9

I would like to extract the highest value from ozone, Solar.R, Wind...

Also, if possible how would I sort Solar.R or any column of this data frame in descending order

I tried

max(ozone, na.rm=T)

which gives me the highest value in the dataset.

I have also tried

max(subset(ozone,Ozone))

but got "subset" must be logical."

I can set an object to hold the subset of each column, by the following commands

ozone <- subset(ozone, Ozone >0)
max(ozone,na.rm=T) 

but it gives the same value of 334, which is the max value of the data frame, not the column.

Any help would be great, thanks.

Answer 1

Similar to colMeans, colSums, etc, you could write a column maximum function, colMax, and a column sort function, colSort.

colMax <- function(data) sapply(data, max, na.rm = TRUE)
colSort <- function(data, ...) sapply(data, sort, ...)

I use ... in the second function in hopes of sparking your intrigue.

Get your data:

dat <- read.table(h=T, text = "Ozone Solar.R Wind Temp Month Day
1     41     190  7.4   67     5   1
2     36     118  8.0   72     5   2
3     12     149 12.6   74     5   3
4     18     313 11.5   62     5   4
5     NA      NA 14.3   56     5   5
6     28      NA 14.9   66     5   6
7     23     299  8.6   65     5   7
8     19      99 13.8   59     5   8
9      8      19 20.1   61     5   9")

Use colMax function on sample data:

colMax(dat)
#  Ozone Solar.R    Wind    Temp   Month     Day 
#   41.0   313.0    20.1    74.0     5.0     9.0

To do the sorting on a single column,

sort(dat$Solar.R, decreasing = TRUE)
# [1] 313 299 190 149 118  99  19

and over all columns use our colSort function,

colSort(dat, decreasing = TRUE) ## compare with '...' above