CODEWITHSUNDEEP
rmax
Al V
Al V

Reputation: 1286

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

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.

Upvotes: 76

Views: 334368

Answers (10)

rrs
rrs

Reputation: 9903

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)

Upvotes: 14

eddy85br
eddy85br

Reputation: 294

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))

Upvotes: 4

S.ElBahloul
S.ElBahloul

Reputation: 75

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 ...

Upvotes: 1

Rich Scriven
Rich Scriven

Reputation: 99331

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

Upvotes: 65

imharindersingh
imharindersingh

Reputation: 196

Assuming that your data in data.frame called maxinozone, you can do this

max(maxinozone[1, ], na.rm = TRUE)

Upvotes: 2

markcodd
markcodd

Reputation: 71

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 ~

Upvotes: 3

WallyTaylor
WallyTaylor

Reputation: 31

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

Upvotes: 2

WheresTheAnyKey
WheresTheAnyKey

Reputation: 878

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)),]

Upvotes: 52

akrun
akrun

Reputation: 887118

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

Upvotes: 4

ccapizzano
ccapizzano

Reputation: 1616

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

Upvotes: 8

Related Questions