[JAVA] filter, map, reduce with js and python (There are also arrow expressions, lambda expressions, comprehension expressions)

Introduction

I make a web application with python and it always mixes, so make a note.

JavaScript

Full version

var orig = [{id: '0000', value: 0},
            {id: '0001', value: 1},
            {id: '0002', value: 2}];
 
// filter
var filtered = orig.filter( function(el,idx,ary) {
  return el.id=='0001';
});
// [{id: '0001', value: 0}]
 
// map
var mapped = orig.map( function(el,idx,ary) {
  return el.value;
});
// [0, 1, 2]
 
// reduce
var reduced = mapped.reduce( function(hist,el,idx,ary) {
  return hist+el;
});
// 3
 
//Direct rewrite
$.each(orig, function(idx,el) {
  el.value += 100;
});
// [{id: '0000', value: 100},
//  {id: '0001', value: 101},
//  {id: '0002', value: 102}]

El is each element, idx is an index, and ary is the original array. idx and ary of filter, map and reduce can be omitted.

Arrow type

// filter
var filtered2 = orig.filter( el => el.id=='0001' );
 
// map
var mapped2 = orig.map( el => el.value );
 
// reduce:lambda expression
var reduced2 = mapped2.reduce( (hist,el) => hist+el );
 
//Direct rewrite
$.each(orig, (idx,el) => { el.value+100 } );

hist of reduce is the execution result of the calculation so far.

Python

lambda expression

orig = [{'id': '0000', 'value': 0},
        {'id': '0001', 'value': 1},
        {'id': '0002', 'value': 2}]
 
# filter
filtered = filter(lambda el: el['id']=='0001', orig)
 
# map
mapped = map(lambda el: el['value'], orig)
 
# reduce
reduced = reduce(lambda hist,el: hist+el, mapped)

Intensional expression

# filter
filtered2 = [ el for el in orig if el['id']=='0001' ]
 
# map
mapped2 = [ el['value'] for el in orig ]

Other cautions

How to access the object

--JavaScript is ʻobject.key --Python is ʻobject ['key']

About JavaScript arrow expressions

//Uninflected word
function(param1, ..., paramN) { statements }
(param1, ..., paramN) => { statements }
 
//If you want to return the value{}Can be omitted.
function(param1, ..., paramN) { return expression; }
(param1, ..., paramN) => { return expression; }
(param1, ..., paramN) => expression
 
//With one argument()Can be omitted.
(param) => { statements }
param => { statements }