>So, I have three questions: is it only a date format issue or am I
missing something else? If it is a date format issue, then, >how would
it be possible to convert my dates in "YYyy-mm-dd" into "yymmdd"? and
finally what loop functions or steps > could I take to create MCPs for
the animals every two weeks.
The error is not a date format issue, as the date is not required for
the calculation of the mcp. As the error message indicates, you need
five relocations or more to compute a minimum convex polygon. That is,
if you type:
any(table(all.id)<5)
If it returns TRUE, this means that for some animals, you have less than
5 relocations, and so you cannot compute a MCP. To identify the animals
that are characterized by 5 relocations or more, try:
ta <- table(all.id)<5
ta[ta<5]
And so, you can remove these animals, if you want to calculate a MCP for
each one:
out <- names(ta[ta<5])
pc <- mcp(all.xy[!(all.id%in%out),], factor(all.id[!(all.id%in%out)])
plot(pc)
Now concerning the loop every two weeks, it is hard to describe you what
to do without any data or precision on what you expect exactly... What
are the limits of the "pairs of weeks"? are they the same for all
animals? are you able to build a variable indicating the id of the
"pairs of weeks" for each relocation (e.g. "2007-09-04" is in the "pair"
1, etc.)? We need more details...
HTH,
Clément Calenge
--
Clément CALENGE
Cellule d'appui à l'analyse de données
Office national de la chasse et de la faune sauvage
Saint Benoist - 78610 Auffargis
tel. (33) 01.30.46.54.14
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