performance - Very slow R loop -

i trying populate column follows:

at t-1: if nav(t-1) - hwm(t-1) >0

then @ t: hwm(t) = nav(t) otherwise: hwm(t) = hwm(t-1)

my r skills quite elementary , following loop, though works, excruciatingly slow (150,000 observations)

for (i in 1:length(e$hwm)) {   print(i)   hwm[e$t>2][i] <- ifelse( nav_lag1[e$t>2][i] - hwm_lag1[e$t>2][i] > 0 ,                            nav_lag1[e$t>2][i] ,                            hwm_lag1[t>2[i] )   hwm_lag1[i] <-lag(hwm,1)[i] } 

any suggestions make process more efficient?

thank much.

here have:

zz <- "t   nav          hwm         nav_lag1    hwm_lag1 1          1000         na          na          na  2          1200         1000        1000        na  3          1400         na          1200        na  4          1200         na          1400        na  5          1100         na          1200        na  5          1000         na          1100        na " 

here get:

zz <- "t   nav          hwm         nav_lag1   hwm_lag1 1          1000         na          na         na  2          1200         1000        1000       1000  3          1400         1200        1200       1000  4          1200         1400        1400       1200 5          1100         1400        1200       1400 5          1000         1400        1100       1400"  data <- read.table(text=zz, header = true)