map Has No Key-Delete Function: The Rebuild Pattern and the weak_map Reset Pattern

1. There Is No Remove: Where Did It Go?

People coming to Verse from Blueprint hit "delete a key" and reflexively hunt for the Remove node — Blueprint Maps plainly have one — only to find Verse has none anywhere, and writing it anyway gets slapped down by Compile. This isn't a missing feature; it's by design: Verse's map, like its array, is a whole you can't edit in place — there is no "pry out one slot where it sits." Every "modification" you make to a variable actually builds a new table and swaps it in whole.

Follow that worldview and the right way to "delete" surfaces on its own: build a new table without that key. The community calls it the rebuild pattern, and there's a YouTube tutorial dedicated to packaging it as a function (the f-icon kind in your My Blueprint panel), ready to call whenever you need it.

2. The Rebuild Pattern: Filter + Refill

The routine is three steps: create a fresh empty table; roll-call the old one with a ForEach Loop, hanging a filter condition on the loop header to skip the key being deleted; write each remaining key-value pair into the new table, then replace the whole table. Packaged as a function, it looks like this:

using { /Fortnite.com/Devices }
using { /UnrealEngine.com/Temporary/Diagnostics }

cleanup_device := class(creative_device):

    var Scores:[string]int = map{"Bubbles" => 10, "Archie" => 5, "Troublemaker" => 99}

    # Returns a new table without the KeyToRemove row
    RemoveKey(Source:[string]int, KeyToRemove:string):[string]int =
        var Result:[string]int = map{}
        for (K -> V : Source, K <> KeyToRemove):
            if (set Result[K] = V) {}
        Result

    OnBegin<override>()<suspends>:void =
        set Scores = RemoveKey(Scores, "Troublemaker")
        Print("{Scores.Length} players left")

Three details worth chewing on: first, for (K -> V : Source, K <> KeyToRemove) is just a ForEach Loop, and what hangs after the comma is a filter condition — <> reads "not equal" — effectively wiring "skip the key being deleted" straight into the loop header; second, writing into the new table uses this lesson's old friend if (set Result[K] = V) {} — writing a value into a map has to go through a Branch; third, set Scores = RemoveKey(...) hands the entire new table to the variable in one go (whole-table replacement), not a write to some key, so no Branch needed. The lone Result on the function's last line is how the value gets passed out as this function's return — the last node's output wired straight to Return, no explicit return call. Once the game starts (Event BeginPlay) and it runs, the log prints "2 players left" — the Troublemaker has been escorted out of the registry.

3. weak_map's Predicament: Can't Rebuild, Can Only Reset

The rebuild pattern has a prerequisite: the table must be roll-callable (iterable). But map's close cousin weak_map (the vehicle for cross-session save data — see the other extra page) precisely can't be roll-called — you can't "filter the old table," so the rebuild pattern breaks down on the spot. So how do you clear out one player's save data?

On the Epic forums, developer Kasity's answer is the whole-entry reset: rather than deleting the row, overwrite it with a brand-new, factory-reset record. For example, when a player leaves the game, reset their weak_map entry back to its initial state. He also stresses a key line of defense: confirm the player is still present before doing anything, or you'll trigger the ErrRuntime_WeakMapInvalidKey runtime error.

using { /Verse.org/Simulation }

# Player stats table (see extra page 3 for the persistence recipe)
player_stats_table := class<final><persistable>:
    Score:int = 0

var StatsTable:weak_map(player, player_stats_table) = map{}

# Call from the player-leave callback: overwrite this player's record with a default instance
ResetPlayer(Target:player):void =
    if (Target.IsActive[]):  # Verify against the Verse API Reference
        if (set StatsTable[Target] = player_stats_table{}) {}

Graph read-through: first declare a "player stats" data structure (marked <persistable>, meaning it can be saved), holding a single Score field. Then declare a weak_map keyed by player. ResetPlayer is a function: an outer Branch first confirms the player is still present (Target.IsActive[]); only once confirmed does the inner Branch overwrite that player's entry with a "fresh from the factory" record.

player_stats_table{} is the "build a brand-new one from the defaults" spelling — every field back to factory settings, effectively the same as "delete that row and open a fresh one." Both routines now stand at their posts: the regular map you can roll-call deletes rows precisely via rebuild; the un-roll-callable weak_map zeroes whole entries via reset.

Sources

Compiled from community tutorials and the Epic developer forums:

▸ How to Remove a Key from a Map in Verse (YouTube Tutorial) ↗
▸ How do we remove player stats from weak map? (Epic Developer Forums) ↗