Поділитися через

List functions

  • Стаття

These functions create and manipulate list values.

Information

Name Description
List.Count Returns the number of items in a list.
List.NonNullCount Returns the number of items in a list excluding null values
List.IsEmpty Returns whether a list is empty.

Selection

Name Description
List.Alternate Returns a list with the items alternated from the original list based on a count, optional repeatInterval, and an optional offset.
List.Buffer Buffers the list in memory. The result of this call is a stable list, which means it will have a determinimic count, and order of items.
List.Distinct Filters a list down by removing duplicates. An optional equation criteria value can be specified to control equality comparison. The first value from each equality group is chosen.
List.FindText Searches a list of values, including record fields, for a text value.
List.First Returns the first value of the list or the specified default if empty. Returns the first item in the list, or the optional default value, if the list is empty. If the list is empty and a default value is not specified, the function returns.
List.FirstN Returns the first set of items in the list by specifying how many items to return or a qualifying condition provided by countOrCondition.
List.InsertRange Inserts items from values at the given index in the input list.
List.IsDistinct Returns whether a list is distinct.
List.Last Returns the last set of items in the list by specifying how many items to return or a qualifying condition provided by countOrCondition.
List.LastN Returns the last set of items in a list by specifying how many items to return or a qualifying condition.
List.MatchesAll Returns true if all items in a list meet a condition.
List.MatchesAny Returns true if any item in a list meets a condition.
List.Positions Returns a list of positions for an input list.
List.Range Returns a count items starting at an offset.
List.Select Selects the items that match a condition.
List.Single Returns the single item of the list or throws an Expression.Error if the list has more than one item.
List.SingleOrDefault Returns a single item from a list.
List.Skip Skips the first item of the list. Given an empty list, it returns an empty list. This function takes an optional parameter countOrCondition to support skipping multiple values.

Transformation functions

Name Description
List.Accumulate Accumulates a result from the list. Starting from the initial value seed this function applies the accumulator function and returns the final result.
List.Combine Merges a list of lists into single list.
List.ConformToPageReader This function is intended for internal use only.
List.RemoveRange Returns a list that removes count items starting at offset. The default count is 1.
List.RemoveFirstN Returns a list with the specified number of elements removed from the list starting at the first element. The number of elements removed depends on the optional countOrCondition parameter.
List.RemoveItems Removes items from list1 that are present in list2, and returns a new list.
List.RemoveLastN Returns a list with the specified number of elements removed from the list starting at the last element. The number of elements removed depends on the optional countOrCondition parameter.
List.Repeat Returns a list that repeats the contents of an input list count times.
List.ReplaceRange Returns a list that replaces count values in a list with a replaceWith list starting at an index.
List.RemoveMatchingItems Removes all occurrences of the given values in the list.
List.RemoveNulls Removes null values from a list.
List.ReplaceMatchingItems Replaces occurrences of existing values in the list with new values using the provided equationCriteria. Old and new values are provided by the replacements parameters. An optional equation criteria value can be specified to control equality comparisons. For details of replacement operations and equation criteria, go to Parameter values.
List.ReplaceValue Searches a list of values for the value and replaces each occurrence with the replacement value.
List.Reverse Returns a list that reverses the items in a list.
List.Split Splits the specified list into a list of lists using the specified page size.
List.Transform Performs the function on each item in the list and returns the new list.
List.TransformMany Returns a list whose elements are projected from the input list.

Membership functions

Since all values can be tested for equality, these functions can operate over heterogeneous lists.

Name Description
List.AllTrue Returns true if all expressions in a list are true
List.AnyTrue Returns true if any expression in a list in true
List.Contains Returns true if a value is found in a list.
List.ContainsAll Returns true if all items in values are found in a list.
List.ContainsAny Returns true if any item in values is found in a list.
List.PositionOf Finds the first occurrence of a value in a list and returns its position.
List.PositionOfAny Finds the first occurrence of any value in values and returns its position.

Set operations

Name Description
List.Difference Returns the items in list 1 that do not appear in list 2. Duplicate values are supported.
List.Intersect Returns a list from a list of lists and intersects common items in individual lists. Duplicate values are supported.
List.Union Returns a list from a list of lists and unions the items in the individual lists. The returned list contains all items in any input lists. Duplicate values are matched as part of the Union.
List.Zip Returns a list of lists combining items at the same position.

Ordering

Ordering functions perform comparisons. All values that are compared must be comparable with each other. This means they must all come from the same datatype (or include null, which always compares smallest). Otherwise, an Expression.Error is thrown.

Comparable data types include:

  • Number
  • Duration
  • DateTime
  • Text
  • Logical
  • Null
Name Description
List.Max Returns the maximum item in a list, or the optional default value if the list is empty.
List.MaxN Returns the maximum values in the list. The number of values to return or a filtering condition must be specified.
List.Median Returns the median item from a list.
List.Min Returns the minimum item in a list, or the optional default value if the list is empty.
List.MinN Returns the minimum values in a list. The number of values to return or a filtering condition may be specified.
List.Sort Returns a sorted list using comparison criterion.
List.Percentile Returns one or more sample percentiles corresponding to the given probabilities.

Averages

These functions operate over homogeneous lists of Numbers, DateTimes, and Durations.

Name Description
List.Average Returns an average value from a list in the datatype of the values in the list.
List.Mode Returns an item that appears most commonly in a list.
List.Modes Returns all items that appear with the same maximum frequency.
List.StandardDeviation Returns the standard deviation from a list of values. List.StandardDeviation performs a sample based estimate. The result is a number for numbers, and a duration for DateTimes and Durations.

Addition

These functions work over homogeneous lists of Numbers or Durations.

Name Description
List.Sum Returns the sum from a list.

Numerics

These functions only work over numbers.

Name Description
List.Covariance Returns the covariance from two lists as a number.
List.Product Returns the product from a list of numbers.

Generators

These functions generate list of values.

Name Description
List.Dates Returns a list of date values from size count, starting at start and adds an increment to every value.
List.DateTimes Returns a list of datetime values from size count, starting at start and adds an increment to every value.
List.DateTimeZones Returns a list of of datetimezone values from size count, starting at start and adds an increment to every value.
List.Durations Returns a list of durations values from size count, starting at start and adds an increment to every value.
List.Generate Generates a list of values.
List.Numbers Returns a list of numbers from size count starting at initial, and adds an increment. The increment defaults to 1.
List.Random Returns a list of count random numbers, with an optional seed parameter.
List.Times Returns a list of time values of size count, starting at start.

Parameter values

Occurrence specification

Sort order

Equation criteria

Equation criteria for list values can be specified as either:

  • A function value that is either:
    • A key selector that determines the value in the list to apply the equality criteria.
    • A comparer function that is used to specify the kind of comparison to apply. Built in comparer functions can be specified—go to Comparer functions.
  • A list value that has:
    • Exactly two items.
    • The first element is the key selector as specified above.
    • The second element is a comparer as specified above.

For more information and examples, go to List.Distinct.

Comparison criteria

Comparison criterion can be provided as either of the following values:

  • A number value to specify a sort order. For more information, go to Sort order.
  • To compute a key to be used for sorting, a function of one argument can be used.
  • To both select a key and control order, comparison criterion can be a list containing the key and order.
  • To completely control the comparison, a function of two arguments can be used that returns -1, 0, or 1 given the relationship between the left and right inputs. Value.Compare is a method that can be used to delegate this logic.

For more information and examples, go to List.Sort.

Replacement operations

Replacement operations are specified by a list value. Each item of this list must be:

  • A list value of exactly two items.
  • First item is the old value in the list, to be replaced.
  • Second item is the new value, which should replace all occurrences of the old value in the list.