[R] Finding the two most recent dates

[Dieter Menne]

Nathalie,

your method of sending sample data is fine. 

dt = structure(list(prochi = c("ind_1", "ind_1", "ind_1",
"ind_1", "ind_1", "ind_1", "ind_1", "ind_1",
"ind_1", "ind_1"), date_1st_event = structure(c(14784,
14784, 14784, 14784, 14784, 14784, 14784, 14784, 14784, 14784
), class = "Date"), bp_date = structure(c(12660, 14571, 13392,
13080, 12012, 13080, 13894, 14622, 12654, 13894), class = "Date"),
    SBP = c(135L, 160L, 135L, 153L, 150L, 153L, 151L, 126L, 150L,
    151L), DBP = c(85L, 80L, NA, 79L, 82L, 79L, 76L, 60L, 82L,
    91L)), .Names = c("prochi", "date_1st_event", "bp_date", "SBP",
"DBP"), row.names = 108:117, class = "data.frame")

# The most recent date
iRecent =  which.max(dt$bp_date) # index of record with most recent date
dt[iRecent,]
# ind_1     2010-06-24 2010-01-13 126  60

# To Paul Hiemstra: we have the integer representation of date here
as.integer(dt$bpdate[iRecent])

I believe that the description of your problem is not complete (homework?),
because there is only on subject and one 1st event. So please try to restate
the rest of the problem.

Dieter





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