Subsetting data

nctoolkit has many built in methods for subsetting data. The main method is subset. This let’s you select specific variables, years, months, seasons and timesteps.

Selecting variables

If you want to select specific variables, you would do the following:

ds.subset(variables = ["var1", "var2"])

If you only want to select one variable, you can do this:

ds.subset(variables = "var1")

Selecting years

If you want to select specific years, you can do the following:

ds.subset(years = [2000, 2001])

Again, if you want a single year the following will work:

ds.subset(years = 2000)

The select method allows partial matches for its arguments. So if we want to select the year 2000, the following will work:

ds.subset(year = 2000)

In this case we can also select a range. So the following will work:

ds.subset(years = range(2000, 2010))

Selecting months

You can select months in the same way as years. The following examples will all do the same thing:

ds.subset(months = [1,2,3,4])
ds.subset(months = range(1,5))
ds.subset(mon = [1,2,3,4])

Selecting seasons

You can easily select seasons. For example if you wanted to select winter, you would do the following:

ds.subset(season = "DJF")

Selecting timesteps

You can select specific timesteps from a dataset in a similar manner. For example if you wanted to select the first two timesteps in a dataset the following two methods will work:

ds.subset(time = [0,1])
ds.subset(time = range(0,2))

Geographic subsetting

If you want to select a geographic subregion of a dataset, you can use subset. This method will select all data within a specific longitude/latitude box. You just need to supply the minimum longitude and latitude required. In the example below, a dataset is cropped with longitudes between -80 and 90 and latitudes between 50 and 80:

ds.subset(lon = [-80, 90], lat = [50, 80])