Buy Terms

Given

set.seed(171124)

buy.term <- function(n)
    floor(rgamma(n, 5, 1))

terms <- matrix(buy.term(30), 10, 3)
colnames(terms) <- LETTERS[1:3]

init.buy <- c('2017-11-01', '2017-11-14', '2017-11-23')
terms

##        A B C
##  [1,]  3 5 6
##  [2,]  4 1 4
##  [3,] 11 8 4
##  [4,]  4 5 3
##  [5,]  3 1 2
##  [6,]  2 3 7
##  [7,]  1 2 5
##  [8,]  3 3 7
##  [9,]  1 4 4
## [10,]  8 3 8

Code

# to date format
init.dates <- init.buy %>% as.Date()

# add terms
ret <- terms %>% apply(2, cumsum) %>% t() + init.dates

# reshape back to matrix
ret <- append(init.dates, ret) %>%
        as.character() %>%
        matrix(nrow = 11, byrow = T)

# copy back ABC
colnames(ret) <- colnames(terms)

ret

##       A            B            C           
##  [1,] "2017-11-01" "2017-11-14" "2017-11-23"
##  [2,] "2017-11-04" "2017-11-19" "2017-11-29"
##  [3,] "2017-11-08" "2017-11-20" "2017-12-03"
##  [4,] "2017-11-19" "2017-11-28" "2017-12-07"
##  [5,] "2017-11-23" "2017-12-03" "2017-12-10"
##  [6,] "2017-11-26" "2017-12-04" "2017-12-12"
##  [7,] "2017-11-28" "2017-12-07" "2017-12-19"
##  [8,] "2017-11-29" "2017-12-09" "2017-12-24"
##  [9,] "2017-12-02" "2017-12-12" "2017-12-31"
## [10,] "2017-12-03" "2017-12-16" "2018-01-04"
## [11,] "2017-12-11" "2017-12-19" "2018-01-12"