## Problem

You want to sort a vector, matrix, or data frame.

## Solution

### Vectors

``````# Make up a randomly ordered vector
v <- sample(101:110)

# Sort the vector
sort(v)
#>   101 102 103 104 105 106 107 108 109 110

# Reverse sort
sort(v, decreasing=TRUE)
#>   110 109 108 107 106 105 104 103 102 101
``````

### Data frames

To sort a data frame on one or more columns, you can use the `arrange` function from `plyr` package, or use R’s built-in functions. The `arrange` function is much easier to use, but does require the external package to be installed.

``````# Make a data frame
df <- data.frame (id=1:4,
weight=c(20,27,24,22),
size=c("small", "large", "medium", "large"))
df

library(plyr)

# Sort by weight column. These have the same result.
arrange(df, weight)       # Use arrange from plyr package
df[ order(df\$weight), ]   # Use built-in R functions
#>   id weight   size
#> 1  1     20  small
#> 2  4     22  large
#> 3  3     24 medium
#> 4  2     27  large

# Sort by size, then by weight
arrange(df, size, weight)         # Use arrange from plyr package
df[ order(df\$size, df\$weight), ]  # Use built-in R functions
#>   id weight   size
#> 4  4     22  large
#> 2  2     27  large
#> 3  3     24 medium
#> 1  1     20  small

# Sort by all columns in the data frame, from left to right
df[ do.call(order, as.list(df)), ]
# In this particular example, the order will be unchanged
``````

Note that the `size` column is a factor and is sorted by the order of the factor levels. In this case, the levels were automatically assigned alphabetically (when creating the data frame), so large is first and small is last.

#### Reverse sort

The overall order of the sort can be reversed with the argument `decreasing=TRUE`.

To reverse the direction of a particular column, the method depends on the data type:

• Numbers: put a `-` in front of the variable name, e.g. `df[ order(-df\$weight), ]`.
• Factors: convert to integer and put a `-` in front of the variable name, e.g. `df[ order(-xtfrm(df\$size)), ]`.
• Characters: there isn’t a simple way to do this. One method is to convert to a factor first and then sort as above.
``````# Reverse sort by weight column. These all have the same effect:
arrange(df, -weight)                      # Use arrange from plyr package
df[ order(df\$weight, decreasing=TRUE), ]  # Use built-in R functions
df[ order(-df\$weight), ]                  # Use built-in R functions
#>   id weight   size
#> 2  2     27  large
#> 3  3     24 medium
#> 4  4     22  large
#> 1  1     20  small

# Sort by size (increasing), then by weight (decreasing)
arrange(df, size, -weight)         # Use arrange from plyr package
df[ order(df\$size, -df\$weight), ]  # Use built-in R functions
#>   id weight   size
#> 2  2     27  large
#> 4  4     22  large
#> 3  3     24 medium
#> 1  1     20  small

# Sort by size (decreasing), then by weight (increasing)
# The call to xtfrm() is needed for factors
arrange(df, -xtfrm(size), weight)         # Use arrange from plyr package
df[ order(-xtfrm(df\$size), df\$weight), ]  # Use built-in R functions
#>   id weight   size
#> 1  1     20  small
#> 3  3     24 medium
#> 4  4     22  large
#> 2  2     27  large
``````