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POAvoiding repetition using lenses whilst deep-copying into Map values
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  1. POAvoiding repetition using lenses whilst deep-copying into Map values
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    copied!<p>I have an immutable data structure where I have nested values in Maps, like so:</p> <pre><code>case class TradingDay(syms: Map[String, SymDay] = Map.empty) case class SymDay(sym: String, traders: Map[String, TraderSymDay] = Map.empty) case class TraderSymDay(trader: String, sym: String, trades: List[Trade] = Nil) </code></pre> <p>Separately I have a list of all trades over the day, and I want to generate the <code>TradingDay</code> structure, where</p> <pre><code>case class Trade(sym: String, trader: String, qty: Int) </code></pre> <p>I am trying to figure out how I would update this structure with lenses (see appendix) by folding through my trades:</p> <pre><code>(TradingDay() /: trades) { (trd, d) =&gt; def sym = trd.sym def trader = trd.trader import TradingDay._ import SymDay._ import TraderSymDay._ val mod = for { _ &lt;- (Syms member sym).mods( _ orElse some(SymDay(sym))) _ &lt;- (Syms at sym andThen Traders member trader).mods( _ orElse some(TraderSymDay(trader, sym))) _ &lt;- (Syms at sym andThen (Traders at trader) andThen Trades).mods( trd :: _) x &lt;- init } yield x mod ! d } </code></pre> <p>This works; but I'm wondering whether I could be less repetitive (in terms of adding to a map and then modifying the value at the key of a map. It doesn't seem that much less annoying than the associated deep-copy.</p> <p><strong>Appendix - the lenses</strong></p> <pre><code>object TradingDay { val Syms = Lens[TradingDay, Map[String, SymDay]](_.syms, (d, s) =&gt; d.copy(syms = s)) } object SymDay { val Traders = Lens[SymDay, Map[String, TraderSymDay]](_.traders, (d, t) =&gt; d.copy(traders = t)) } object TraderSymDay { val Trades = Lens[TraderSymDay, List[Trade]](_.trades, (d, f) =&gt; d.copy(trades = f)) } </code></pre>
 

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