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--- manipulating_tables_and_lookup_tables [2026/07/25 03:50]
hermann
+++ manipulating_tables_and_lookup_tables [2026/07/25 04:29] (current)
hermann
@@ Line 162: / Line 162: @@
         NumberString key 1;
         NumberValue value 1;
+    }};
+    _ := Print { initialMessage = message } {{ }};
+}};
+</code>
+**Example** — a table with more than one value column. Nothing new is needed: call ''GetTableValue'' once per value column and combine the results:
+<code>
+myTable := Table [
+    "CityId*", "Population", "Area",
+, 667137, 125,
+, 39398, 6
+];
+allKeys := GetTableKeys myTable;
+_ := ForEach allKeys {{
+    key := Step;
+    population := GetTableValue myTable key "Population";
+    area := GetTableValue myTable key "Area";
+    message := CreateString "(CityId: <v1>, Population: <v2>, Area: <v3>)" {{
+        NumberValue key 1;
+        NumberValue population 2;
+        NumberValue area 3;
     }};
@@ Line 236: / Line 262: @@
 // citySubTable will be the Year*/Price pairs for city 4534272.
 citySubTable := GetTableFromKey priceTableByCity 4534272;
+</code>
+**Example** — printing every entry of a table with more than one key column. [[Get Table Keys]] only ever iterates the //first// key column, so a table with several needs one nested loop per extra key: peel off a sub-table for each ''Year'', then iterate the ''City'' key within it:
+<code>
+priceTable := Table [
+    "Year*", "City*", "Price",
+, 4534272, 1200,
+, 5483552, 1453,
+, 4534272, 4332,
+, 5483552, 233
+];
+yearKeys := GetTableKeys priceTable;
+_ := ForEach yearKeys {{
+    year := Step;
+    pricesInYear := GetTableFromKey priceTable year;
+    cityKeys := GetTableKeys pricesInYear;
+    _ := ForEach cityKeys {{
+        city := Step;
+        price := GetTableValue pricesInYear city "Price";
+        message := CreateString "(Year: <v1>, City: <v2>, Price: <v3>)" {{
+            NumberValue year 1;
+            NumberValue city 2;
+            NumberValue price 3;
+        }};
+        _ := Print { initialMessage = message } {{ }};
+    }};
+}};
+</code>
+===== Storing results across a loop =====
+A [[Mux Table]] or [[Mux Lookup Table]] can carry a Table or Lookup Table across the iterations of a loop, the same way [[Mux Value]] carries a single value — see [[ego_script#carrying_and_selecting_values_across_iterations|Carrying and selecting values across iterations]]. Each iteration reads the mux's current output, adds a row to it with ''AddTableRow'', and feeds the result back in as the mux's ''feedback'' input for the next iteration, building up a result table one row at a time.
+The accumulated table is read after the loop the same way any container's internal result is read from outside it: a functor after the loop simply takes the accumulator's feedback variable as an input. There's nothing special about this — the loop is guaranteed to finish before anything depending on it runs, per [[basic_data_flow|Basic Data Flow]].
+<code>
+sourceLookup := LookupTable [
+    "Key" "Value",
+667137,
+39398,
+181045
+];
+emptyResults := Table [
+    "CityId*#real", "DoubledPopulation#real"
+];
+_ := ForEach sourceLookup {{
+    accumulated := MuxTable emptyResults nextAccumulated;
+    key := Step;
+    population := GetLookupTableValue sourceLookup key;
+    doubled := $ [ $population * 2 ];
+    newRow := AddTupleValue key doubled;
+    nextAccumulated := AddTableRow accumulated newRow;
+}};
+// finalResults holds every row added across all iterations. Use nextAccumulated,
+// not accumulated (the mux's own output), which lags one iteration behind.
+// The Table carrier passes it through, since := always binds a functor call.
+finalResults := Table nextAccumulated;
+</code>
+> **Note:** This is also why ''accumulated'' should never be read again after ''AddTableRow'' consumes it in the same iteration. When exactly one reference to a table's current version remains, Dinamica can update it destructively — modifying the existing storage in place. A second live reference to ''accumulated'' (reading it directly somewhere else, instead of only through ''nextAccumulated'') forces Dinamica to copy the table instead, since the old version now has to stay intact for that other reference. That copy cost repeats every iteration — see [[basic_data_flow|Basic Data Flow]] for this same rule stated generally, beyond just tables.
+**Why this isn't the best approach.** [[basic_data_flow|Basic Data Flow]] documents three conditions under which a loop's iterations can run simultaneously: no mux directly inside the loop, nothing produced inside the loop consumed outside it, and no loop member used as a submodel's output port. A mux-based accumulator like the one above breaks the first condition outright — the mux ties every iteration to the one before it, so the loop can never run as anything but sequential, even when the per-iteration work is otherwise completely independent, as it is above (each row's value depends only on that row's own key).
+When the transformation is this simple — one output row per input row, computed independently — the calculator shorthand already covered in [[calculate_functors#5_lookup_table_operators|Lookup Table Operators]] produces the same result without a loop, a mux, or the sequential cost that comes with one:
+<code>
+doubledResults := % [ %sourceLookup[line] * 2 ] "CityId" "DoubledPopulation" sourceLookup;
 </code>