Using C# and LINQ

Question

I have some funky xml files.  First off, I have values that are not sequential in the file and duplicate values (if they exist) need to be combined, let me give you a visual of the sample input.

<?xml version="1.0"?>
<PRICE_YIELD_ANALYSIS _SeriesNumber="4083" _CollateralStatus="Assumed" _Source="FHLMC" _DealerName="CITIGROUP GLOBAL MARKETS, INC.">
<OCS_GROUP _Number="1" _SettlementDate="2012-07-30" _FirstPaymentDate="2012-08-15">
<PRICE_YIELD_UNIT>
<CLASS _Id="PJ" _AssumedPrice="30.125" _Cap="3.500000" _InitialCouponRate="3.500000" _InitialAccrualPeriod="29" _Floor="0.000000" _Multiplier="1" _OriginalUpb="6365000.000000" _Spread="131.50000"/>
<SCENARIO _PrepaymentSpeedValue="126" _PrepaymentSpeedType="PSA" _IndexRate="1" _IndexName="LIBOR_1MO"/>
<PRICE_YIELD_DETAIL _YieldPct="1.48420"/>
</PRICE_YIELD_UNIT>
<CLASS _Id="PJ" _AssumedPrice="30.125" _Cap="3.500000" _InitialCouponRate="3.500000" _InitialAccrualPeriod="29" _Floor="0.000000" _Multiplier="1" _OriginalUpb="6365000.000000" _Spread="131.50000"/>
<SCENARIO _PrepaymentSpeedValue="126" _PrepaymentSpeedType="PSA" _IndexRate="2" _IndexName="LIBOR_1MO"/>
<PRICE_YIELD_DETAIL _YieldPct="0.51789"/>
</PRICE_YIELD_UNIT>
<PRICE_YIELD_UNIT>
<CLASS _Id="PJ" _AssumedPrice="30.125" _Cap="3.500000" _InitialCouponRate="3.500000" _InitialAccrualPeriod="29" _Floor="0.000000" _Multiplier="1" _OriginalUpb="6365000.000000" _Spread="131.50000"/>
<SCENARIO _PrepaymentSpeedValue="126" _PrepaymentSpeedType="PSA" _IndexRate="3" _IndexName="LIBOR_1MO"/>
<PRICE_YIELD_DETAIL _YieldPct="5.41789"/>
</PRICE_YIELD_UNIT>
<PRICE_YIELD_UNIT>
...

           126%  200%  50%  25%  400%  500% 
           ================================      
1%         1.5   1.5    0.2  3.5   7.6   4.4
2%         0.5   0.5    3.4  5.6   7.8   9.0
3%         5.4   5.4    1.2  2.3   3.4   5.6
4%         2.3   2.3    0.9  8.7   6.5   4.3

they want the output to look like:

                       126%
                       thru
           25%   50%   200%   400%  500% 
           ============================      
1%         3.5   0.2    1.5   7.6   4.4
2%         5.6   3.4    0.5   7.8   9.0
3%         2.3   1.2    5.4   3.4   5.6
4%         8.7   0.9    2.3   6.5   4.3
Is there any way to have linq statement sort by to order these by 
_PrepaymentSpeedValue=
accordingly AND to combine similar columns like 126 and 200%.