`g_quantile(G;S;X;P)`

Returns the quantile for values within a given group.

Function type

Vector only

Syntax

g_quantile(G;S;X;P)
t_quantile(X;P)

Input

Argument	Type	Description
`G`	any	A space- or comma-separated list of column names Rows are in the same group if their values for all of the columns listed in `G` are the same. If `G` is omitted, all rows are considered to be in the same group. If any of the columns listed in `G` contain N/A, the N/A value is considered a valid grouping value.
`S`	integer	The name of a column in which every row evaluates to a 1 or 0, which determines whether or not that row is selected to be included in the calculation If `S` is omitted, all rows will be considered by the function (subject to any prior row selections). If any of the values in `S` are neither 1 nor 0, an error is returned.
`X`	any numeric type	A column name
`P`	integer or decimal	A column name or an expression evaluating to a numeric value that represents a probability for each row of the table

Return Value

For every row in each group defined by G (and for those rows where S=1, if specified), g_quantile returns a numeric value corresponding to the smallest value of X such that random draws from the valid (non-N/A) values of X within the group would be less than or equal to X with a probability no greater than P. The result is the same data type as X.

For example, g_quantile(G;S;X;0.5) is the (lower) median of X.

Sample Usage

<base table="pub.doc.samples.ref.func.g_func_sample_usage_two_values"/>
<willbe name="g_quantile_1" value="g_quantile(state;include;value1;0.25)"/>
<willbe name="g_quantile_2" value="g_quantile(state city;include;value2;0.25)"/>

Example

Let's use the Hourly U.S. Weather (1990) table (pub.demo.weather.hourly90) to demonstrate the use of g_quantile(G;S;X;P).

Let's say we want to find the 0.25 quantile with respect to hourly precipitation for a particular day. In other words, we want to find the smallest value of hourly precipitation such that it and all values lower than it constitute 25% of the values within the group.

For demonstration purposes, let's select one particular day at one particular station, and we'll display only those columns that are relevant to this example:

<sel value="(date=19900224)"/>
<sel value="(id=25339)"/>
<colord cols="id,date,hour,prec"/>

This will give us the following:

Note: prec is the hourly precipitation measured in .01 inches.

Let's create a computed column for the results of g_quantile(G;S;X;P). Since we've already selected the rows that we want for our group, we can omit the G parameter. We'll also omit the S parameter, since we want to consider all rows in this group. We'll specify the prec column for X, since we want to find the quantile with respect to hourly precipitation, and we'll specify .25 for the P parameter so that we obtain the 0.25 quantile.

<willbe name="quantile" value="g_quantile(;;prec;0.25)"/>

This will give us the following:

This new column shows that 25% of the values in the group are less than or equal to 9. So, for the 24 hours that we have selected in this group, 6 had .09 inches or less of rain that day.

If we sort the prec column in descending order and look at the lowest 6 values, we can see that they all have values of 9 or less:

<sort col="prec" dir="down"/>

Additional Information

The t_ version of this function defaults the G argument and omits the S argument. The default for G is set at table load time based on the organization of the table.