投稿時間:2022-10-17 06:16:56 RSSフィード2022-10-17 06:00 分まとめ(18件)

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海外TECH	DEV Community	Javascript Array Reduce Method	https://dev.to/smpnjn/javascript-array-reduce-method-3a3	Javascript Array Reduce MethodThe Javascript reduce method is a recursive way to perform a computation based on every element in array while also taking into consideration the previous element in the array It accepts a function which can also be used to further process elements of the array based on logic of your choosing It is quite useful for summing arrays or merging string based arrays For example we could turn an array into a string like this let myArray hello world welcome let reduceString myArray reduce previousElement currentElement gt return previousElement currentElement console log reduceString hello world welcome In a similar vein we could use it to add up all the numbers in an array and return a single number let myArray let reduceString myArray reduce previousElement currentElement gt previousElement currentElement console log reduceString The reduce method callback functionThe callback function used in reduce actually has arguments You are not required to use any but the first two are the two you will usually want The format of the function looks like this Array reduce previousElement currentElement currentIndex array gt Do something with the array s data initialValue Let s look at what previousElement currentElement currentIndex array and initialValue all mean previousElementThis is self explanatory It represents the previous element from the current one we are iterating through The reduce function will usually start at the index so that a previous element does exist If you have defined an initialValue then this value will be used and the reduce function will begin at index using the initialValue as the previousValue currentElementThis is the current element that is being iterated through by reduce currentIndexSince arrays don t consist of just indexes and often have useful data in them we also have the ability to get the current index being iterated through This will return the indexed number representing the current element s position in the array Expect standard array indexes from this argument arrayThis will return the entire array which can be useful if you plan to manipulate the array using reduce or if you want to compute based on other elements in the array initialValueIf provided this will be the previousElement for index As mentioned this are all optional but they all provide a useful way to manipulate and calculate the return value for your reduce method Mutating the Array in reduceIf you try to mutate the array in reduce it could lead to some interesting behaviour so there are a few edge cases you should consider when thinking about reduce For example if you change an array element somewhere ahead of your current element the reduction will still work as expected For example adding to myArray currentIndex will still produce the expected value let myArray let reduceFunction myArray reduce prevValue currentValue currentIndex gt myArray currentIndex return prevValue currentValue console log reduceFunction However trying to add values to an array while running reduce will not work For example below I use push to add one element to the array for each element in the array This would of course lead to an infinite loop so Javascript arrests the function and only processes the values that were in the array at the point when we ran reduce let myArray let reduceFunction myArray reduce prevValue currentValue currentIndex gt myArray push return prevValue currentValue console log reduceFunction Note on Single Value ArraysIf your array only contains one value and you don t use initialValue the reduce function will return the single value from that array and not call the callback function For example let myArray cat let reduceFunction myArray reduce prevValue currentValue gt return currentValue console log reduceFunction cat does not have exclamation mark even though we tried to add it Summing and Combining Values in an Object ArrayYou might have already expected this behaviour but if you have an array of objects you can reference the child properties of each elements object to make calculations For example to add up all the ages below let myArray age age age age let reduceFunction myArray reduce prevValue currentValue gt return prevValue currentValue age console log reduceFunction You might ve noticed a few weird things here which is why it s useful to work through this example We have to define an initialValue since initially prevValue is age but afterwards prevValue is a number That means we keep types consistent Since every time we run reduce it returns the a value for the current item in the array element we use prevValue rather than prevValue age prevValue age is undefined since reduce returns a number each time ConclusionThe reduce method is a really useful way to combine everything in an array or produce new arrays of your choosing It s powerful and recursive so be careful when using it on large data sets If you liked this I also wrote an article here on the slice method	2022-10-16 20:26:15
Apple	AppleInsider - Frontpage News	iPhone 14 Pro lead times dip below iPhone 13 Pro as moderation continues	https://appleinsider.com/articles/22/10/16/iphone-14-pro-lead-times-dip-below-iphone-13-pro-as-moderation-continues?utm_medium=rss	iPhone Pro lead times dip below iPhone Pro as moderation continuesDelivery lead times of the iPhone Pro models have dipped below their iPhone equivalents at this stage of release analysts claim while demand for the iPhone remains modest iPhone ProIn the sixth week of the Apple Product Availability Tracker by JP Morgan the Pro models of iPhone are seeing lead times moderate from the fifth week s data According to the tracker lead times for the iPhone Pro Max have leveled off to be at par with the Pro Read more	2022-10-16 20:34:33
ニュース	@日本経済新聞 電子版	三井住友海上、ギグワーカー向け金融　まず車両ローン https://t.co/r9WCIVlqrT	https://twitter.com/nikkei/statuses/1581743209759199233	三井住友海上	2022-10-16 20:25:43
ニュース	@日本経済新聞 電子版	月曜朝が憂鬱じゃない職場に　「働きがい」高める14選 https://t.co/1yt5gvUHSM	https://twitter.com/nikkei/statuses/1581737181852602368	働きがい	2022-10-16 20:01:46
ニュース	@日本経済新聞 電子版	プライーベート市場に警戒を　ひた迫る危機の足音 https://t.co/BGdhclBy6n	https://twitter.com/nikkei/statuses/1581737180606582784	警戒	2022-10-16 20:01:45
ニュース	BBC News - Home	UN condemns 'deeply distressing' discovery of 92 naked migrants at Greece-Turkey border	https://www.bbc.co.uk/news/world-europe-63278122?at_medium=RSS&at_campaign=KARANGA	border	2022-10-16 20:09:37
ニュース	BBC News - Home	Garth Crooks' Team of the Week: Salah, Toney, Mount, Silva, Martinez	https://www.bbc.co.uk/sport/football/63279726?at_medium=RSS&at_campaign=KARANGA	crooks	2022-10-16 20:32:00
ニュース	BBC News - Home	Rugby League World Cup: Joseph Manu scores superb solo try	https://www.bbc.co.uk/sport/av/rugby-league/63278912?at_medium=RSS&at_campaign=KARANGA	warrington	2022-10-16 20:19:48
ビジネス	ダイヤモンド・オンライン - 新着記事	売れなくなったPC、コロナ特需に終焉 - WSJ発	https://diamond.jp/articles/-/311385	終焉	2022-10-17 05:25:00
ビジネス	ダイヤモンド・オンライン - 新着記事	「キラキラ大家・共食い大家」に気をつけろ！富裕層をカモにする悪徳不動産投資サロンの最新手口 - 円安・金利高・インフレに勝つ！最強版 富裕層の節税＆資産防衛術	https://diamond.jp/articles/-/311258	「キラキラ大家・共食い大家」に気をつけろ富裕層をカモにする悪徳不動産投資サロンの最新手口円安・金利高・インフレに勝つ最強版富裕層の節税資産防衛術女性向けシェアハウス「かぼちゃの馬車」が社会問題化したが、不動産を取り巻く世界では次々に新たな手法が生み出され、被害に遭う人が絶えない。	2022-10-17 05:25:00
ビジネス	ダイヤモンド・オンライン - 新着記事	EYジャパンの貴田CEOに直撃！「監査とコンサルを分離」する狙いとは？ - 会計士・税理士・社労士 経済3士業の豹変	https://diamond.jp/articles/-/310962		2022-10-17 05:20:00
ビジネス	ダイヤモンド・オンライン - 新着記事	年収1000万円超企業「5年後の年収」独自予想ランキング！【27社】2位東京建物147万円増、1位は？ - 高年収＆高収益 勝ち組企業大解剖！儲けの秘密と本当の待遇	https://diamond.jp/articles/-/310572	浮き彫り	2022-10-17 05:15:00
ビジネス	ダイヤモンド・オンライン - 新着記事	セブン＆アイのそごう・西武売却が八方ふさがり、買い手ヨドバシの「無理難題」に労組猛反発 - セブン解体	https://diamond.jp/articles/-/311247	セブンアイのそごう・西武売却が八方ふさがり、買い手ヨドバシの「無理難題」に労組猛反発セブン解体米投資ファンドのフォートレス・インベストメント・グループが優先交渉権を得ているセブンアイ・ホールディングス傘下のそごう・西武の売却交渉が、「八方ふさがり」の様相を呈している。	2022-10-17 05:10:00
ビジネス	ダイヤモンド・オンライン - 新着記事	米国の金利上昇、銀行に追い風なのは今のうち - WSJ発	https://diamond.jp/articles/-/311386	金利上昇	2022-10-17 05:08:00
ビジネス	ダイヤモンド・オンライン - 新着記事	タワマン節税も最高裁否決、富裕層の節税策は全部塞がれ「詐欺」が残った【富裕層税理士座談会1】 - 円安・金利高・インフレに勝つ！最強版 富裕層の節税＆資産防衛術	https://diamond.jp/articles/-/311257	防衛	2022-10-17 05:05:00
ビジネス	電通報 | 広告業界動向とマーケティングのコラム・ニュース	アスリートブレーンズ為末大の「緩急自在」vol.28	https://dentsu-ho.com/articles/8357	緩急自在	2022-10-17 06:00:00
ビジネス	東洋経済オンライン	会議中に｢スマホ｣を見ることで失う大切なモノ 相手に｢無礼だ｣と思われないちょっとしたコツ | リーダーシップ・教養・資格・スキル | 東洋経済オンライン	https://toyokeizai.net/articles/-/624404?utm_source=rss&utm_medium=http&utm_campaign=link_back	東洋経済オンライン	2022-10-17 05:40:00
ビジネス	東洋経済オンライン	学び直しの切り札｢無料講座｣を使い倒すノウハウ 大学と同等の講義や双方向の授業など内容も多彩 | 最新の週刊東洋経済 | 東洋経済オンライン	https://toyokeizai.net/articles/-/625741?utm_source=rss&utm_medium=http&utm_campaign=link_back	東洋経済オンライン	2022-10-17 05:20:00