SAS - Calculating the present value of future interest and amortization payments of loans

I would like to calculate the present value (PV) of future interest and amortization payments on loans (flat amortization and annuity) in a dataset. The discount rate should be the inflation e.g. 2 per cent. I have seen the finance function in SAS, but it requires each cashflow which are difficult due to the nature of the dataset.

E.g. if you borrow 100,000 for 100 month (flat amortization) you will repay (amortization) 1,000 each month. But due to inflation (e.g. 2 per cent) the 100 month repayment is not the same as the 1 month in real terms. The same goes for the interest cost.

In the end I would like to have columns after my dataset that show the PV of all future interest and amortization payments.

If possible I would like to have the solution in a data step.

Example of my dataset

data have;
    call streaminit(12345);
    do i = 1 to 5;
        loanAmount = abs(rand("normal", 300E3, 200E3));
        interestRateNominalAnnual = abs(rand('normal',0.05,0.05));
        maturityMonth = abs(rand("normal", 120, 24));
        output;
    end;
    format loanAmount comma10. interestRateNominalAnnual 5.2 maturityMonth 3.0;
run;

Want

options cmplib=work.ORBA;
proc fcmp outlib=work.ORBA.pv; * Present value;
    subroutine pvLoan(  /* input */
                        loanAmount,
                        maturityMonth,
                        interestRateAnnual,
                        inflationAnnual,

                        /* output */
                        amortizationSumAnnuity,
                        interestSumAnnuity,
                        invoiceSumAnnuity,

                        amortizationSumFlat,
                        interestSumFlat,
                        invoiceSumFlat,

                        pvAmortizationSumAnnuity,
                        pvInterestSumAnnuity,
                        pvInvoiceSumAnnuity,

                        pvAmortizationSumFlat,
                        pvInterestSumFlat,
                        pvInvoiceSumFlat);

    outargs amortizationSumAnnuity,     interestSumAnnuity,     invoiceSumAnnuity,
            amortizationSumFlat,        interestSumFlat,        invoiceSumFlat, 
            pvAmortizationSumAnnuity,   pvInterestSumAnnuity,   pvInvoiceSumAnnuity,
            pvAmortizationSumFlat,      pvInterestSumFlat,      pvInvoiceSumFlat;

        if missing(loanAmount) or missing(maturityMonth) or missing(interestRateAnnual) then 
            do;
                pvAmortizationSumAnnuity    = .;
                pvInterestSumAnnuity        = .;
                pvInvoiceSumAnnuity         = .;
                pvAmortizationSumFlat       = .;
                pvInterestSumFlat           = .;
                pvInvoiceSumFlat            = .;
            end;
        else
            do;
                inflationMonth  = sum(exp((log(sum(1,inflationAnnual)))/12),-1);

                do maturityPeriod = 1 to maturityMonth;
*                   ------------------------------------------------------------------------------------------;
*                               ANNUITY;
*                   ------------------------------------------------------------------------------------------;
                    fv                      = 0; * Specifies the future value after the last payment is made;
                    paymentDueDate          = 0; * Specifies whether the payments occur at the beginning or end of a period. 0 represents the end-of-period payments;

*                   NOMINAL VALUE;
*                   If the interest rate is zero you only amortize. Equal to flat amortization;
                    if interestRateAnnual = 0 then 
                        do;
                            amortizationAnnuity         = loanAmount / maturityMonth;
                            interestPaymentAnnuity      = 0;
                            invoiceAnnuity              = sum(amortizationAnnuity, interestPaymentAnnuity);
                        end;
                        else
                            do;
                                amortizationAnnuity     = abs(finance('ppmt', interestRateAnnual/12, maturityPeriod, maturityMonth, loanAmount, paymentDueDate));
                                invoiceAnnuity          = abs(finance('pmt', interestRateAnnual/12, maturityMonth, loanAmount, fv, paymentDueDate));
                                interestPaymentAnnuity  = abs(sum(invoiceAnnuity, - amortizationAnnuity));
                            end;

*                   Cumulative nominal flat amortization;
                    amortizationSumAnnuity      = sum(amortizationSumAnnuity, amortizationAnnuity);
                    interestSumAnnuity          = sum(interestSumAnnuity, interestPaymentAnnuity);
                    invoiceSumAnnuity           = sum(amortizationSumAnnuity, interestSumAnnuity);

*                   PRESENT VALUE;
*                   Present value of the interest and amortization for a annuity;
                    pvAmortizationAnnuity       = amortizationAnnuity    / ((1+inflationMonth)**maturityPeriod);
                    pvInterestAnnuity           = interestPaymentAnnuity / ((1+inflationMonth)**maturityPeriod);
                    pvInvoiceAnnuity            = sum(pvAmortizationAnnuity, pvInterestAnnuity);

*                   Cumulative present value annuity;
                    pvAmortizationSumAnnuity    = sum(pvAmortizationSumAnnuity, pvAmortizationAnnuity);
                    pvInterestSumAnnuity        = sum(pvInterestSumAnnuity, pvInterestAnnuity);
                    pvInvoiceSumAnnuity         = sum(pvAmortizationSumAnnuity, pvInterestSumAnnuity);

*                   ------------------------------------------------------------------------------------------;
*                               FLAT AMORTIZATION;
*                   ------------------------------------------------------------------------------------------;
*                   NOMINAL VALUE;
*                   Payment in period n;
                    amortizationFlat        = loanAmount / maturityMonth;
                    interestPaymentFlat     = (sum(loanAmount, -amortizationFlat*(maturityPeriod-1)) * interestRateAnnual/12);
                    invoiceFlat             = sum(amortizationFlat, interestPaymentFlat);

*                   Cumulative nominal flat amortization;
                    amortizationSumFlat     = sum(amortizationSumFlat, amortizationFlat);
                    interestSumFlat         = sum(interestSumFlat, interestPaymentFlat);
                    invoiceSumFlat          = sum(amortizationSumFlat, interestSumFlat);

*                   PRESENT VALUE;
*                   Present value of the interest and amortization for flat amortization;
                    pvAmortizationFlat      = amortizationFlat    / ((1+inflationMonth)**maturityPeriod);
                    pvInterestFlat          = interestPaymentFlat / ((1+inflationMonth)**maturityPeriod);
                    pvInvoiceFlat           = sum(pvAmortizationFlat, pvInterestFlat);

*                   Cumulative present value flat amortization;
                    pvAmortizationSumFlat   = sum(pvAmortizationSumFlat, pvAmortizationFlat);
                    pvInterestSumFlat       = sum(pvInterestSumFlat, pvInterestFlat);
                    pvInvoiceSumFlat        = sum(pvAmortizationSumFlat, pvInterestSumFlat);
                end;
            end;
    endsub;
run;

data have;
    call streaminit(12345);
    do i = 1 to 5;
        loanAmount          = abs(floor(rand("normal", 300E3, 200E3)));
        maturityMonth       = abs(floor(rand("normal", 120, 24)));
        interestRateAnnual  = abs(rand('normal',0.05,0.05));
        output;
    end;
    format loanAmount maturityMonth comma10. interestRateAnnual percent10.2;
    drop i;
run;

data want;
set have;
*   Call the subroutine and performe the calculations;
    call pvLoan(    /* input */
                    loanAmount,
                    maturityMonth,
                    interestRateAnnual,
                    0.02,
                    /* output */
                    amortizationSumAnnuity,
                    interestSumAnnuity,
                    invoiceSumAnnuity,

                    amortizationSumFlat,
                    interestSumFlat,
                    invoiceSumFlat,

                    pvAmortizationSumAnnuity,
                    pvInterestSumAnnuity,
                    pvInvoiceSumAnnuity,

                    pvAmortizationSumFlat,
                    pvInterestSumFlat,
                    pvInvoiceSumFlat);
    format _numeric_ comma20. interestRateAnnual percent5.2;
run;