dfsql

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
  

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 <col>
  

  sort icpsr_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
  

• aggregate

  <aggregate> : <expr>? -> <expr>
  

  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.