percentile

../../_images/PERCENTILE.png

Computes a set of percentiles of a given input Fieldset. A percentile is a number such that the given percentage of a distribution is equal to or below it. For instance, the median is the 50th percentile - 50% of the values are equal to or below it. The generated fields can simp

Note

This function performs the same task as the Percentile icon in Metview’s user interface. It accepts its parameters as keyword arguments, described below.

percentile(**kwargs)

Computes a set of percentiles of a given input Fieldset.

Parameters

  • source (str, default: "off") – Specifies the GRIB file path and name. Alternatively, parameter data can be used. If both source and data are specified data takes precedence.

  • data (Fieldset) – Specifies the GRIB data required for the application. Takes precedence over source.

  • percentiles (number or list[number], default: 10.0) – Specifies a list of percentile values from 0 to 100.

  • interpolation ({"nearest_neighbour", "linear"}, default: "nearest_neighbour") –

    Specifies the interpolation method used to compute the percentiles. Given a list of numbers V, the algorithm used to compute a percentile is the following. First, the the rank (R) of a P-th percentile is computed. This is done using the following formula: R = P/100 x (N + 1) where P is the desired percentile and N is the number of input fields. Then, the percentile itself is computed:

    • If R is an integer, the P-th percentile will be the number with rank R.

    • If R is not an integer, the P-th percentile is computed by interpolation as follows:

      • If interpolation is “nearest_neighbour”, the following equation is used: P-th = V[int(R + 0.5)]

      • If interpolation is “linear”, the following steps are used:

        1. Define IR as the integer portion of R

        2. Define FR as the fractional portion of R

        3. Find the scores with Rank IR and with Rank IR + 1, e.g. V[IR] and V[IR+1]

        4. Interpolate by multiplying the difference between the scores by FR and add the result to the lower score, e.g. Pth = FR * (V[IR+1] - V[IR]) + V[IR]

  • compute_if_missing_present ({"on", "off"}, default: "on") –

    Specifies how to handle the presence of missing values in the input data:

    • ”on”: for each grid point, the percentiles are computed using only the non-missing values

    • ”off”: for each grid point, if there are any missing values, the result for that point will be a missing value

Return type

Fieldset

Notebooks using metview.percentile

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Computing and plotting ENS data (GRIB)