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Update comparisons with data.table info (#2725)
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@eloualiche
eloualiche authored May 13, 2021
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Expand Up @@ -240,6 +240,70 @@ The table below compares more advanced commands:
| DataFrame as input | `summarize(df, head(across(), 2))` | `combine(d -> first(d, 2), df)` |
| DataFrame as output | `summarize(df, tibble(value = c(min(x), max(x))))` | `combine(df, :x => (x -> (value = [minimum(x), maximum(x)],)) => AsTable)` |


## Comparison with the R package data.table

The following table compares the main functions of DataFrames.jl with the R package data.table (version 1.14.1).

```R
library(data.table)
df <- data.table(grp = rep(1:2, 3), x = 6:1, y = 4:9,
z = c(3:7, NA), id = letters[1:6])
df2 <- data.table(grp=c(1,3), w = c(10,11))
```

| Operation | data.table | DataFrames.jl |
|:-----------------------------------|:-------------------------------------------------|:---------------------------------------------|
| Reduce multiple values | `df[, .(mean(x))]` | `combine(df, :x => mean)` |
| Add new columns | `df[, x_mean:=mean(x) ]` | `transform!(df, :x => mean => :x_mean)` |
| Rename column (in place) | `setnames(df, "x", "x_new")` | `rename!(df, :x => :x_new)` |
| Rename multiple columns (in place) | `setnames(df, c("x", "y"), c("x_new", "y_new"))` | `rename!(df, [:x, :y] .=> [:x_new, :y_new])` |
| Pick columns as dataframe | `df[, .(x, y)]` | `select(df, :x, :y)` |
| Pick column as a vector | `df[, x]` | `df[!, :x]` |
| Remove columns | `df[, -"x"]` | `select(df, Not(:x))` |
| Remove columns (in place) | `df[, x:=NULL]` | `select!(df, Not(:x))` |
| Remove columns (in place) | `df[, c("x", "y"):=NULL]` | `select!(df, Not([:x, :y]))` |
| Pick & transform columns | `df[, .(mean(x), y)]` | `select(df, :x => mean, :y)` |
| Pick rows | `df[ x >= 1 ]` | `filter(:x => >=(1), df)` |
| Sort rows (in place) | `setorder(df, x)` | `sort!(df, :x)` |
| Sort rows | `df[ order(x) ]` | `sort(df, :x)` |

### Grouping data and aggregation

| Operation | data.table | DataFrames.jl |
|:----------------------------|:--------------------------------------------------|:------------------------------------------|
| Reduce multiple values | `df[, mean(x), by=id ]` | `combine(groupby(df, :id), :x => mean)` |
| Add new columns (in place) | `df[, x_mean:=mean(x), by=id]` | `transform!(groupby(df, :id), :x => mean)`|
| Pick & transform columns | `df[, .(x_mean = mean(x), y), by=id]` | `select(groupby(df, :id), :x => mean, :y)`|

### More advanced commands

| Operation | data.table | DataFrames.jl |
|:----------------------------------|:-------------------------------------------------------------------------------------------|:----------------------------------------------------------------------------|
| Complex Function | `df[, .(mean(x, na.rm=TRUE)) ]` | `combine(df, :x => x -> mean(skipmissing(x)))` |
| Transform certain rows (in place) | `df[x<=0, x:=0]` | `df.x[df.x .<= 0] .= 0` |
| Transform several columns | `df[, .(max(x), min(y)) ]` | `combine(df, :x => maximum, :y => minimum)` |
| | `df[, lapply(.SD, mean), .SDcols = c("x", "y") ]` | `combine(df, [:x, :y] .=> mean)` |
| | `df[, lapply(.SD, mean), .SDcols = patterns("*x") ]` | `combine(df, names(df, r"^x") .=> mean)` |
| | `df[, unlist(lapply(.SD, function(x) c(max=max(x), min=min(x)))), .SDcols = c("x", "y") ]` | `combine(df, ([:x, :y] .=> [maximum minimum])...)` |
| Multivariate function | `df[, .(cor(x,y)) ]` | `transform(df, [:x, :y] => cor)` |
| Row-wise | `df[, min_xy := min(x, y), by = 1:nrow(df)]` | `transform!(df, [:x, :y] => ByRow(min))` |
| | `df[, argmax_xy := which.max(.SD) , .SDcols = patterns("*x"), by = 1:nrow(df) ]` | `transform!(df, AsTable(r"^x") => ByRow(argmax))` |
| DataFrame as output | `df[, .SD[1], by=grp]` | `combine(groupby(df, :grp), first)` |
| DataFrame as output | `df[, .SD[which.max(x)], by=grp]` | `combine(groupby(df, :grp), sdf -> sdf[argmax(sdf.x), :])` |

### Joining data frames

| Operation | data.table | DataFrames.jl |
|:----------------------|:------------------------------------------------|:--------------------------------|
| Inner join | `merge(df, df2, on = "grp")` | `innerjoin(df, df2, on = :grp)` |
| Outer join | `merge(df, df2, all = TRUE, on = "grp")` | `outerjoin(df, df2, on = :grp)` |
| Left join | `merge(df, df2, all.x = TRUE, on = "grp")` | `leftjoin(df, df2, on = :grp)` |
| Right join | `merge(df, df2, all.y = TRUE, on = "grp")` | `rightjoin(df, df2, on = :grp)` |
| Anti join (filtering) | `df[!df2, on = "grp" ]` | `antijoin(df, df2, on = :grp)` |
| Semi join (filtering) | `merge(df1, df2[, .(grp)]) ` | `semijoin(df, df2, on = :grp)` |


## Comparison with Stata (version 8 and above)

The following table compares the main functions of DataFrames.jl with Stata:
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