Fastest by column sort in R

Question

I have a data frame `full` from which I want to take the last column and a column `v`. I then want to sort both columns on `v` in the fastest way possible. `full` is read in from a csv but this can be used for testing (included some NAs for realism): ``` n <- 200000 full <- data.frame(A = runif(n, 1, 10000), B = floor(runif(n, 0, 1.9))) full[sample(n, 10000), 'A'] <- NA v <- 1 ``` I have `v` as one here, but in reality it could change, and `full` has many columns. I have tried sorting data frames, data tables and matrices each with `order` and `sort.list` (some ideas taken from this thread). The code for all these: ``` # DATA FRAME ord_df <- function() { a <- full[c(v, length(full))] a[with(a, order(a[1])), ] } sl_df <- function() { a <- full[c(v, length(full))] a[sort.list(a[[1]]), ] } # DATA TABLE require(data.table) ord_dt <- function() { a <- as.data.table(full[c(v, length(full))]) colnames(a)[1] <- 'values' a[order(values)] } sl_dt <- function() { a <- as.data.table(full[c(v, len…

Accepted Answer

I don't know if it's better to put this sort of thing in as an edit but it seems more like answer so here will do. Updated test functions:

```
n <- 1e7
full <- data.frame(A = runif(n, 1, 10000), B = floor(runif(n, 0, 1.9)))
full[sample(n, 100000), 'A'] <- NA

fdf <- full
fma <- as.matrix(full)
fdt <- as.data.table(full)
setnames(fdt, colnames(fdt)[1], 'values')

# DATA FRAME
ord_df <- function() { fdf[order(fdf[1]), ] }
sl_df <- function() { fdf[sort.list(fdf[[1]]), ] }

# DATA TABLE
require(data.table)
ord_dt <- function() { fdt[order(values)] }

key_dt <- function() {
  setkey(fdt, values) 
  fdt
}

# MATRIX
ord_mat <- function() { fma[order(fma[, 1]), ] }
sl_mat <- function() { fma[sort.list(fma[, 1]), ] }
```

Results (using a different computer, R 2.13.1 and `data.table` 1.8.2):

```
         ord_df  sl_df   ord_dt  key_dt  ord_mat sl_mat
Min.     37.56   20.86   2.946   2.249   20.22   20.21
1st Qu.  37.73   21.15   2.962   2.255   20.54   20.59
Median   38.43   21.74   3.002   2.280   21.05   20.82
Mean     38.76   21.75   3.074   2.395   21.09   20.95
3rd Qu.  39.85   22.18   3.151   2.445   21.48   21.42
Max.     40.36   23.08   3.330   2.797   22.41   21.84
```

So data.table is the clear winner. Using a key is faster than ordering, and has a nicer syntax as well I'd argue. Thanks for the help everyone.

Fastest by column sort in R

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