sequences, empty if "by" not conforming
Generate sequences, but unlike "seq", return NULL, when "seq" would generate a backward sequence. This function is useful for for-loops, when empty loops are required in the case where by is in the "wrong" direction, see examples.
seqm(from, to, by=1)
from |
starting value of sequence. |
to |
(maximal) end value of the sequence. |
by |
increment of the sequence. |
NULL, if (to-from)*by <0, otherwise
usual result of seq i.e. seq.default.
Christian W. Hoffmann <christian@echoffmann.ch>
seqm(12,4,-1) # 12 11 10 9 8 7 6 5 4
seqm(12,4,2) # NULL
lo <- 1; up <- 3
for (ii in lo:up) {
cat(ii," ")
for (kk in seqm(lo,ii-1)) {
cat(" ",kk) # do-in-lower-triangle
}
cat(" diag") # do-something-on-the-diagonal
for (kk in seqm(ii+1,up)) {
cat(" :",kk) # do-in-upper-traingle
}
cat("\n")
}
# 1 diag : 2 : 3
# 2 1 diag : 3
# 3 1 2 diagPlease choose more modern alternatives, such as Google Chrome or Mozilla Firefox.