I have a data matrix of order 2000 x 20, and I want to choose a specific order of entire rows from the matrix, for example, 1st,7th, 8th, 14th, 15th, 21th, 22th, is such a sequence of rows until the last 2000th rows.
[1, 7, 8, 14, 15, 21, 22, ...]
Manually it's very difficult to select such a sequence, is there is an alternative to do the same task in R? are the for looping is helpful in solving such a problem.
Using the updated question data, something like:
cumsum(rep(c(1,6), 2000/7))
# [1] 1 7 8 14 15
# ...
#[566] 1981 1982 1988 1989 1995
Since your pattern is +1/+6 up until 2000, you can repeat the two values c(1,6) as many times as sum(c(1,6)) goes in to 2000, and then take a cumulative sum.
You can define your sequence first, using e.g. sequence, and then subset using [].
n = 2000 / 7
s = sequence(nvec = c(1, rep(2,n)), from = c(1, 7*1:n))
# s
# [1] 1 7 8 14 15 21 22 28 29 35 36 42 43 49 50 56 57 63 64 70 71 ...
yourMatrix[s, ]
sequence creates a sequence of sequences of length nvec and of starting point from.