murex rocks

Welcome

About

Install

Change Log

Blog

Technical Docs

Language Tour

Interactive Shell

Rosetta Stone

User Guide

Open Source

Discuss

Contribute

Source Code

Search Site

For Each In Map (formap)

Iterate through a map or other collection of data

Description

formap is a generic tool for iterating through a map, table or other sequences of data similarly like a foreach. In fact formap can even be used on array too.

Unlike foreach, formap’s default output is str, so each new line will be treated as a list item. This behaviour will differ if any additional flags are used with foreach, such as --jmap.

Usage

formap writes a list:

<stdin> -> foreach variable { code-block } -> <stdout>

formap writes to a buffered JSON map:

<stdin> -> formap --jmap key value { code-block (map key) } { code-block (map value) } -> <stdout>

Examples

First of all lets assume the following dataset:

set json people={
    "Tom": {
        "Age": 32,
        "Gender": "Male"
    },
    "Dick": {
        "Age": 43,
        "Gender": "Male"
    },
    "Sally": {
        "Age": 54,
        "Gender": "Female"
    }
}

We can create human output from this:

» $people -> formap key value { out "$key is $value[Age] years old" }
Sally is 54 years old
Tom is 32 years old
Dick is 43 years old

Please note that maps are intentionally unsorted so you cannot guarantee the order of the output produced even if the input has been superficially set in a specific order.

With --jmap we can turn that structure into a new structure:

» $people -> formap --jmap key value { $key } { $value[Age] }
{
    "Dick": "43",
    "Sally": "54",
    "Tom": "32"
} 

Flags

• --jmap Write a json map to stdout instead of an array

Detail

formap can also work against arrays and tables as well. However foreach is a much better tool for ordered lists and tables can look a little funky when when there are more than 2 columns. In those instances you’re better off using [ (index) to specify columns and then tabulate for any data transformation.

Meta values

Meta values are a JSON object stored as the variable $.. The meta variable will get overwritten by any other block which invokes meta values. So if you wish to persist meta values across blocks you will need to reassign $., eg

%[1..3] -> foreach {
    meta_parent = $.
    %[7..9] -> foreach {
        out "$(meta_parent.i): $.i"
    }
}

The following meta values are defined:

• i: iteration number

See Also

• Define Variable (set): Define a variable (typically local) and set it’s value
• Exit Block (break): Terminate execution of a block within your processes scope
• For Each In List (foreach): Iterate through an array
• For Loop (for): A more familiar iteration loop to existing developers
• Get Item ([ Index ]): Outputs an element from an array, map or table
• Loop While (while): Loop until condition false
• Transformation Tools (tabulate): Table transformation tools
• json: JavaScript Object Notation (JSON)

---

This document was generated from builtins/core/structs/formap_doc.yaml.