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 

Answer 2

To get the max of any column you want something like:

max(ozone$Ozone, na.rm = TRUE) 

To get the max of all columns, you want:

apply(ozone, 2, function(x) max(x, na.rm = TRUE)) 

And to sort:

ozone[order(ozone$Solar.R),] 

Or to sort the other direction:

ozone[rev(order(ozone$Solar.R)),]