Various types of subsetting of a time series. Allows subsetting by index
values (unlike `window`

). Also allows extraction of the
values of a specific season or subset of seasons in each year. For example,
to extract all values for the month of May from a time series.

## Arguments

- x
a univariate time series to be subsetted

- subset
optional logical expression indicating elements to keep; missing values are taken as false.

`subset`

must be the same length as`x`

.- month
Numeric or character vector of months to retain. Partial matching on month names used.

- quarter
Numeric or character vector of quarters to retain.

- season
Numeric vector of seasons to retain.

- start
Index of start of contiguous subset.

- end
Index of end of contiguous subset.

- ...
Other arguments, unused.

## Value

If `subset`

is used, a numeric vector is returned with no ts
attributes. If `start`

and/or `end`

are used, a ts object is
returned consisting of x[start:end], with the appropriate time series
attributes retained. Otherwise, a ts object is returned with frequency equal
to the length of `month`

, `quarter`

or `season`

.

## Details

If character values for months are used, either upper or lower case may be
used, and partial unambiguous names are acceptable. Possible character
values for quarters are `"Q1"`

, `"Q2"`

, `"Q3"`

, and
`"Q4"`

.

## Examples

```
plot(subset(gas,month="November"))
subset(woolyrnq,quarter=3)
#> Time Series:
#> Start = 1965.5
#> End = 1994.5
#> Frequency = 1
#> [1] 6633 6730 6946 6915 7190 7105 6840 7819 7045 5540 5906 5505 5318 5466 5696
#> [16] 5341 5464 5129 5524 6080 6540 6339 6590 6077 5146 5127 5222 4954 5309 6396
subset(USAccDeaths, start=49)
#> Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
#> 1977 7792 6957 7726 8106 8890 9299 10625 9302 8314 8850 8265 8796
#> 1978 7836 6892 7791 8192 9115 9434 10484 9827 9110 9070 8633 9240
```