====== Many to One Mapping with Non-Summation Aggregation Rule ======
The map tool can perform an index mapping in which multiple elements of informant X are mapped to the same element of informant Y.  To aggregate multiple elements into one, the map tool sums the values of the composite elements.  However, there may be a need to use a different aggregation function such as minimum, maximum, or average.  

The following example demonstrates how to implement this logic.

===== Background =====
In this example, the variable indexed by the informant unitID will be mapped to a variable indexed by the informant plantID.  The contents of these informants are:
<code>
plantID[]: set
 version: 3
 desc:    localinformant plantID[] = create (; object=set, data="Plant1 Plant2")
 data:    2 elements
-----------------------------------
1     Plant1          
2     Plant2          

unitID[]: set
 version: 3
 desc:    localinformant unitID[] = create (; object=set, data="Unit1 Unit2 Unit3 Unit4 Unit5")
 data:    5 elements
-----------------------------------
1     Unit1           
2     Unit2           
3     Unit3           
4     Unit4           
5     Unit5           
</code>

The variable unitComYr contains commissioning years by unitID

{{:howtos:toolcoding:unitcomyr.png|}}

===== Implementation =====
1. Create the following desired mapping from unitID to plantID is:\\

Unit1 -> Plant1\\
Unit2 -> Plant2\\
Unit3 -> Plant1\\
Unit4 -> Plant1\\
Unit5 -> Plant2

<code>
local unitToPlantMap[uid] = create (; dataType=integer, dim=unitID, data="1 2 1 1 2")
</code>


2. Create a mask that will expand unitComYr to include plantID

<code>
local pid[pid,pid] = diag (1.0; dim=plantID)
local plantIDMask[uid,pid] = boolne (dimtran (pid[pid,pid]; map1=unitToPlantMap[uid], newDims=1, checkData=off),0)
</code>
{{:howtos:toolcoding:plantidmask.png|}}

<code>
local unitComYrx[uid,pid] = unitComYr[uid] * plantIDMask[uid,pid]
</code>
{{:howtos:toolcoding:unitcomyrx.png|}}


3. Add offset to remove 0's before taking minimum
<code>
local unitComYry[uid,pid] = booleq (unitComYrx[uid,pid],0) * 9999 + unitComYrx[uid,pid]
</code>


4. Use coordmin to create a variable that contains online date, which is the earliest commissioning year of the units that comprise the plant, by plantId
<code>
local plantOnlineDate[pid] = coordmin (reorder (unitComYry[uid,pid]; plantID, unitID); numDims=1)
</code>
{{:howtos:toolcoding:plantonlinedate.png|}}

Click {{:howtos:toolcoding:mapmin.t|here}} to download the tool file that encapsulates the above example.