Using Aggregate to perform summary calculcations on selected fields
To use the Aggregate transform

Add the Aggregate node to the job diagram.

On the Node properties tab, choose fields to group together by selecting the dropdown field (optional). You can select more than one field at a time or search for a field name by typing in the search bar.
When fields are selected, the name and datatype are shown. To remove a field, choose 'X' on the field.

Choose Aggregate another column. It is required to select at least one field.

Choose a field in the Field to aggregate dropdown.

Choose the aggregation function to apply to the chosen field:

avg  calculates the average

countDistinct  calculates the number of unique nonnull values

count  calculates the number of nonnull values

first  returns the first value that satisfies the 'group by' criteria

last  returns the last value that satisfies the 'group by' criteria

kurtosis  calculates the the sharpness of the peak of a frequencydistribution curve

max  returns the highest value that satisfies the 'group by' criteria

min  returns the lowest value that satisfies the 'group by' criteria

skewness  measure of the asymmetry of the probability distribution of a normal distribution

stddev_pop  calculates the population standard deviation and returns the square root of the population variance

sum  the sum of all values in the group

sumDistinct  the sum of distinct values in the group

var_samp  the sample variance of the group (ignores nulls)

var_pop  the population variance of the group (ignores nulls)
