问题
I have a array with following content:
> head(MEAN)
1901DJF 1901JJA 1901MAM 1901SON 1902DJF 1902JJA
-0.45451556 -0.72922229 -0.17669396 -1.12095590 -0.86523850 -0.04031273
This should be a time series with seasonal mean values from 1901 to 2009. The problem is that the generated column heads are strictly alphabetically ordered. However, in terms of season this doesn't make to much sense, e.g. JJA (june, july, august) is leading MAM (march, april, may).
How could I switch each MAM and JJA entry of the array?
PS: MEAN is generated applying tapply on the data.frame pdsi
> head(pdsi)
date scPDSI month seas seasyear
1 1901-01-01 -0.10881074 Jan DJF 1901DJF
2 1901-02-01 -0.22287750 Feb DJF 1901DJF
3 1901-03-01 -0.12233192 Mär MAM 1901MAM
4 1901-04-01 -0.04440915 Apr MAM 1901MAM
5 1901-05-01 -0.36334082 Mai MAM 1901MAM
6 1901-06-01 -0.52079030 Jun JJA 1901JJA
>
> MEAN <- tapply(pdsi$scPDSI, ts.pdsi$seasyear, mean, na.rm = T)
May be there is also known a more elegant way to calculate seasonal means...
回答1:
You can change the order of the factor levels:
pdsi[["seasyear"]] = factor(pdsi[["seasyear"]], levels = c("1901DJF", "1901MAM", etc))
回答2:
I think this is a fairly simple way of re-ordering your means, however, it does have the assumption that your data is already ordered chronologically in the data set. So if that holds this should work.
I also created some random data, rather than copying your data, but the results should be the same
seasons = c("1901DJF", "1901MAM", "1901JJA")
seasons = rep(seasons, c(2, 3, 1))
data = data.frame(runif(1:6), seasons)
MEAN = tapply(data[,1], data[,2], mean)
1901DJF 1901JJA 1901MAM
0.5799779 0.3724785 0.6514327
order = unique(seasons)
MEAN[order]
1901DJF 1901MAM 1901JJA
0.5799779 0.6514327 0.3724785
What this does is take the order of seasyear in the data set, and reorders the object MEAN to reflect that order. Again, it assumes your data is chronologically ordered in the raw file, but I think this is a safe assumption. Apologies if it is not the case.
来源：https://stackoverflow.com/questions/18976078/how-to-switch-rows-in-r