dfsql is both an executable binary that can be run, and a library that can be used in Rust programs.

Installing the command-line executable

Assuming you have Rust/Cargo installed, run this command in a terminal:

cargo install dfsql

It will make the dfsql command available in your PATH if you've allowed the PATH to be modified when installing Rust. cargo uninstall dfsql uninstalls.

Adding `dfsql` library as a dependency

Run this command in a terminal, in your project's directory:

cargo add dfsql

To add it manually, edit your project's Cargo.toml file and add to the [dependencies] section:

dfsql = "0.15.1"

The dfsql library will be automatically available globally. Read the dfsql library documentation.

Back to the crate overview.

Readme

`dfsql`

Revision: the standalone count command is replaced with len, so make sure to replace (count) and col "count" with len and col "len" respectively.
- the unary count <col> command is unaffected.

Install

cargo install dfsql

How to run

dfsql --input your.csv --output a-new.csv
# ...or
dfsql -i your.csv -o a-new.csv

REPL

exit/quit: exit the REPL loop.
```
exit
```
undo: undo the previous successful operation.
```
undo
```
reset: reset all the changes and go back to the original data frame.
```
reset
```
schema: show column names and types of the data frame.
```
schema
```
save: save the current data frame to a file.
```
save a-new.csv
```

Statements

select
```
select <expr>*
```
```
select last_name first_name
```
- Select columns "last_name" and "first_name" and collect them into a data frame.
Group by
```
group (<col> | <var>)* agg <expr>*
```
```
group first_name agg (count)
```
- Group the data frame by column "first_name" and then aggregate each group with the count of the members.

filter

filter <expr>

filter first_name = "John"

limit
```
limit <int>
```
```
limit 5
```
reverse
```
reverse
```

sort

sort ((asc | desc | ()) <col>)*

sort icpsr_id

use
```
use <var>
```
```
use other
```
- Switch to the data frame called other.

join

(left | right | inner | full) join <var> on <col> <col>?

left join other on id ID

left join the data frame called other on my column id and its column ID

Expressions

col: reference to a column.

col : (<str> | <var>) -> <expr>

select col first_name

exclude: remove columns from the data frame.

exclude : <expr>* -> <expr>

select exclude last_name first_name

literal: literal values like 42, "John", 1.0, and null.
binary operations
```
select a * b
```
- Calculate the product of columns "a" and "b" and collect the result.
unary operations
```
select -a
```
```
select sum a
```
- Sum all values in column "a" and collect the scalar result.
alias: assign a name to a column.
```
alias : (<col> | <var>) <expr> -> <expr>
```
```
select alias product a * b
```
- Assign the name "product" to the product and collect the new column.

conditional

<conditional> : if <expr> then <expr> (if <expr> then <expr>)* otherwise <expr> -> <expr>

select if class = 0 then "A" if class = 1 then "B" else null

cast: cast a column to either type str, int, or float.
```
cast : <type> <expr> -> <expr>
```
```
select cast str id
```
- Cast the column "id" to type str and collect the result.

Installing the command-line executable

Adding dfsql library as a dependency

Adding `dfsql` library as a dependency