[Experimental] A promise API for data wrangling in JavaScript

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[*] => promise<boolean>

Evaluates to true if the following are satisfied:

• the argument is an object or promise resolving to an object
• the object is not empty (i.e., has at least one key)
• the value of every key is an array (may contain any data type)
• arrays are of equal length

promise<dataTable> => promise<object>

Given a data table, returns a promise for an object containing the following key-value pairs:

• variables: the number of variables (arrays) in the data table
• observations: the number of observations (array length) for each variable

promise<dataTable> => promise<array<string>>

Given a data table, returns a promise for an array of variable names.

promise<dataTable>, string => promise<array>

Given a data table and a variable name, returns a promise for an array containing the variable's observed values.

promise<dataTable>, number:int => promise<object>

Given a data table and a valid index, returns a promise for an object containing the value of each variable at that index, which represents a single observation across all variables in the data set.

promise<dataTable>, [number:int] => promise<dataTable>

Given a data table and an optional output size n (defaults to 5), returns a promise for a data table containing only the first n observations.

promise<dataTable>, function<dataTable, ...[*] => *>, ...[*] => promise<*>

Apply an arbitrary function on a data table, returning a promise for the result.

promise<dataTable>, promise<dataTable>, function<dataTable, dataTable, ...[*] => *>, ...[*] => promise<*>

Apply an arbitrary function on two data tables, returning a promise for the result.

promise<dataTable>, array<string>, function<array, ...[*] => array>, ...[*] => promise<dataTable>

Apply an arbitrary function on one or more variable arrays in a data table, returning a promise for a new data table with the resulting arrays.

promise<dataTable>, array<string>, function<*, ...[*] => *>, ...[*] => promise<dataTable>

Apply an arbitrary function on every observed value for one or more variable arrays in a data table, returning a promise for a new data table with the resulting values.

promise<dataTable>, promise<dataTable> => promise<dataTable>

Assign the variables of two source data tables to a new target (analogous to Object.assign({}, a, b)). The two source data tables must have the same number of observations. If variable names are shared between the sources, the second overwrites the first. Returns a promise for the new combined data table.

promise<dataTable>, array<string> => promise<dataTable>

Given a data table and an array of variable names, returns a promise for a data table containing only the selected variables.

promise<dataTable>, function<object, [number:int], [dataTable] => boolean> => promise<dataTable>

Given a data table and a filtering function, returns a promise for a data table filtered according the return values of the function, where true means keep and false means drop. The filtering function's first parameter is an object containing the value of each variable at index i, the second (optional) parameter is the value of i, and the third (optional) parameter is the data table being filtered. Analogous to Array.prototype.filter.