how to order values with different classes in R

Question

[szp770]

Hi, I have a csv file like this:

order      class      value
1             a             5
2             a             6
3             a             4
4             b             10
5             b              7
6             b              18

now I want to order this by the each class and its values:

order      class      value
3             a             4
1             a             5
2             a             6
5             b              7
4             b             10
6             b              18

how to do this in R? Thanks!

Answer 1

[ATpoint]

#/ Data:
df <- 
data.frame(order=seq(1,6),
           class=rep(c("a", "b"), each=3),
           value=c(5,6,4,10,7,18))

#/ Base R ::: https://stackoverflow.com/questions/1296646/how-to-sort-a-dataframe-by-multiple-columns
df[with(df, order(class, value)), ]

#/ dplyr ::: https://dplyr.tidyverse.org/reference/arrange.html
library(dplyr)
df %>% arrange(class, value)

As usual the base solution is much faster compared to dplyr (tidyverse). Still, with multiple filtering conditions and with operations up- and downstream of this command the tidyverse syntax / verbs can be more convenient to write and easier to read, so exactly what the tidyverse has been developed for (it has not been developed for speed, this is a common misconception from what I understand).

library(microbenchmark)
base=function(x) df[with(df, order(class, value)),]
tidy=function(x) df %>% arrange(class, value)
microbenchmark(base=base(), tidy=tidy())

Unit: microseconds
 expr      min        lq       mean    median       uq      max neval
 base   59.125   71.5165   96.27901   79.3505   88.886 1680.796   100
 tidy 1611.210 1782.8240 1941.95609 1887.5755 1937.872 7368.565   100

[szp770]

thanks. What if the data is stored in a csv file and I don't know eactly how many numbers each class has.

[ATpoint]

I don't know eactly how many numbers each class has.

What does that mean?

Answer 2

[dariober]

I'm on the the data.table camp which is usually faster and, in my opinion, more readable than base R or dplyr. In this case:

df[order(class, value), ]

dplyr (which I haven't really used) seems to have too many dedicated functions and idioms for common tasks, like arrange, filter and I feel I need to re-learn what I already know. I don;t get that with data.table like in this example.

Answer 3

[cpad0112]

> library(sqldf)

> df
  order class value
1     1     a     5
2     2     a     6
3     3     a     4
4     4     b    10
5     5     b     7
6     6     b    18

> sqldf("select * from df order by class, value")
  order class value
1     3     a     4
2     1     a     5
3     2     a     6
4     5     b     7
5     4     b    10
6     6     b    18

> sqldf("select * from df order by class asc, value asc")

[szp770]

that really helps! do you know how to do the reverse order, from the biggest value to the smallest value

[cpad0112]

If you want to sort only values in descending order:

sqldf("select * from df order by class, value desc")

If you want to sort both class and value by desc

sqldf("select * from df order by class desc, value desc")

if you want class to be desc, but value to be in ascening order:

sqldf("select * from df order by class desc, value")

[szp770]

thanks! what if I want value in descending order, but class in a given order, like "b b b a a a c c c " but not "aaa bbb ccc"