How to find the highest value of a column in a data frame in R? - 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)),]

Answer 3

Here's a dplyr solution:
library(dplyr)
# find max for each column
summarise_each(ozone, funs(max(., na.rm=TRUE)))
# sort by Solar.R, descending
arrange(ozone, desc(Solar.R))
UPDATE: summarise_each() has been deprecated in favour of a more featureful family of functions: mutate_all(), mutate_at(), mutate_if(), summarise_all(), summarise_at(), summarise_if()
Here is how you could do:
# find max for each column
ozone %>%
summarise_if(is.numeric, funs(max(., na.rm=TRUE)))%>%
arrange(Ozone)
or
ozone %>%
summarise_at(vars(1:6), funs(max(., na.rm=TRUE)))%>%
arrange(Ozone)

Answer 4

In response to finding the max value for each column, you could try using the apply() function:
> apply(ozone, MARGIN = 2, function(x) max(x, na.rm=TRUE))
Ozone Solar.R Wind Temp Month Day
41.0 313.0 20.1 74.0 5.0 9.0

Answer 5

Another way would be to use ?pmax
do.call('pmax', c(as.data.frame(t(ozone)),na.rm=TRUE))
#[1] 41.0 313.0 20.1 74.0 5.0 9.0

Answer 6

There is a package matrixStats that provides some functions to do column and row summaries, see in the package vignette, but you have to convert your data.frame into a matrix.
Then you run: colMaxs(as.matrix(ozone))

Answer 7

max(may$Ozone, na.rm = TRUE)
Without $Ozone it will filter in the whole data frame, this can be learned in the swirl library.
I'm studying this course on Coursera too ~

Answer 8

Assuming that your data in data.frame called maxinozone, you can do this
max(maxinozone[1, ], na.rm = TRUE)

Answer 9

max(ozone$Ozone, na.rm = TRUE) should do the trick. Remember to include the na.rm = TRUE or else R will return NA.

Answer 10

Try this solution:
Oz<-subset(data, data$Month==5,select=Ozone) # select ozone value in the month of
#May (i.e. Month = 5)
summary(T) #gives caracteristics of table( contains 1 column of Ozone) including max, min ...