[R] remove loop which compares row i to row i-1

[jcrosbie]

I would like to remove a loop to speed up my code. 

I want to remove a loop which references the last row. 

In general I want to a remove a loop which looks something like this:
for 2 to number of rows in a matrix do{
if indextrow-1 is < currentIndexRow then do something. 
}


My R code:

    for (i in 2:length(tUnitsort$Hour)){
      ifelse(tUnitsort[i,4]>=tUnitsort[i-1,4],(tempMC
=tUnitsort[i,7]),tempMC ) #col. 4 = BlockNumber; note tests to see if the
offers have change to the next set of blocks. 
      ifelse(tUnitsort[i,4]>=tUnitsort[i-1,4],(tempAC
=tUnitsort[i,7]-(tUnitsort[i,8]-tUnitsort[i,9])),tempAC )
      tUnitsort$MC[i] <- tempMC
      tUnitsort$AC[i] <- tempAC
      tUnitsort$PercentofMC[i] <- tUnitsort$Size[i]/tempMC
      tUnitsort$PercentofAC[i] <- tUnitsort$AvailableMW[i]/tempAC
    }

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