FieldMappings (arcpy)

Zusammenfassung

The FieldMappings object is a collection of FieldMap objects and it is used as the parameter value for tools that perform field mapping, such as Merge.

Diskussion

Das FieldMappings-Objekt ist eine Sammlung von FieldMap-Objekten und wird als Parameterwert für Werkzeuge für die Feldzuordnung verwendet, beispielsweise Zusammenführen (Merge). Sie können am einfachsten mit diesen Objekten arbeiten, indem Sie zuerst ein FieldMappings-Objekt erstellen und dann die zugehörigen FieldMap-Objekte initialisieren, indem Sie die zu kombinierenden Eingabe-Feature-Classes oder Tabellen hinzufügen. Wenn alle Eingaben bereitgestellt wurden, enthält das FieldMappings-Objekt ein FieldMap-Objekt (bzw. ein Ausgabefeld) für jeden eindeutigen Feldnamen aus allen Eingaben. Sie können diese Liste ändern, indem Sie neue Felder hinzufügen, die Eigenschaften und/oder den Inhalt von Ausgabefeldern ändern oder unerwünschte Ausgabefelder entfernen.

Die Eigenschaften des FieldMap-Objekts enthalten die Anfangs- und die Endposition eines Eingabetextwertes, sodass ein neuer Ausgabewert mit einem Teil eines Eingabewertes erstellt werden kann. Wenn ein FieldMap-Objekt mehrere Eingabefelder aus derselben Tabelle oder Feature-Class enthält, werden die Werte aller Datensätze unter Verwendung der Eigenschaft MergeRule zusammengeführt. Dies ist eine benutzerfreundliche Möglichkeit zum Verbinden von Werten, beispielsweise eines Straßennamens in einem Feld und einer Straßenart, die in einem anderen Feld enthalten ist (z. B. "Eureka" und "Street"). Der joinDelimiter-Eigenschaft eines FieldMap-Objekts wird verwendet, wenn der mergeRule-Wert Join angegeben wird. Als Trennzeichen können beliebige Zeichen verwendet werden, beispielsweise Leerzeichen. Im obigen Beispiel würde damit der Wert "Eureka Street" erstellt.

Syntax

FieldMappings ()

Eigenschaften

Eigenschaft	Erläuterung	Datentyp
fieldCount (Schreibgeschützt)	The number of output fields.	Integer
fieldMappings (Lesen und schreiben)	A list of FieldMap objects that make up the FieldMappings object.	FieldMap
fieldValidationWorkspace (Lesen und schreiben)	The workspace type that defines the rules for attribute field naming. These rules are used when determining the output field names, which are based on the names of the input fields. For example, setting the fieldValidationWorkspace property to the path of a folder on disk containing the input shapefiles will result in the output field names being truncated to 10 characters. Setting the fieldValidationWorkspace property to the path of a file geodatabase will allow for much longer field names. The fieldValidationWorkspace property should be set with a consideration for the output format.	String
fields (Schreibgeschützt)	A list of Field objects. Each field object represents the properties of each output field.	Field

Methodenübersicht

Methode	Erläuterung
addFieldMap (field_map)	Add a field map to the field mappings.
addTable (table_dataset)	Adds a table to the field mappings object.
exportToString ()	Exports the object to its string representation.
findFieldMapIndex (field_map_name)	Find a field map within the field mappings by name.
getFieldMap (index)	Gets a field map from the field mappings.
loadFromString (string)	Restore the object using its string representation. The exportToString method can be used to create a string representation.
removeAll ()	Removes all values and creates an empty object.
removeFieldMap (index)	Removes a field map from the field mappings.
replaceFieldMap (index, value)	Replace a field map within the field mappings.

Methoden

addFieldMap (field_map)

Parameter	Erläuterung	Datentyp
field_map	The field map to add to the field mappings	FieldMap

addTable (table_dataset)

Parameter	Erläuterung	Datentyp
table_dataset	The table to add to the field mappings object.	String

exportToString ()

Rückgabewert

Datentyp	Erläuterung
String	The string representation of the object.

findFieldMapIndex (field_map_name)

Parameter	Erläuterung	Datentyp
field_map_name	Find the field map by name.	String

Rückgabewert

Datentyp	Erläuterung
Integer	The index position of the field map.

getFieldMap (index)

Parameter	Erläuterung	Datentyp
index	The index position of the field map.	Integer

Rückgabewert

Datentyp	Erläuterung
FieldMap	The field map from the field mappings.

loadFromString (string)

Parameter	Erläuterung	Datentyp
string	The string representation of the object.	String

removeAll ()

removeFieldMap (index)

Parameter	Erläuterung	Datentyp
index	The index position of the field map.	Integer

replaceFieldMap (index, value)

Parameter	Erläuterung	Datentyp
index	The index position of the field map to be replaced.	Integer
value	The replacement field map.	FieldMap

Codebeispiel

FieldMappings example

FieldMap objects are often used when there is a need to merge similar datasets into one, all-encompassing dataset. In this example, the feature class Trees and the shapefile Plants.shp are merged into one feature class: Vegetation. Both original feature classes have two attributes: Type and Diameter. These two attributes must be maintained through the merge.

# Import the arcpy module.
import arcpy

# Set the workspace.
arcpy.env.workspace = 'c:/base'

in_file1 = 'data.gdb/Trees'
in_file2 = 'Plants.shp'
output_file = 'data.gdb/Vegetation'

# Create the required FieldMap and FieldMappings objects.
fm_type = arcpy.FieldMap()
fm_diam = arcpy.FieldMap()
fms = arcpy.FieldMappings()

# Get the field names of vegetation type and diameter for both original files.
tree_type = "Tree_Type"
plant_type = "Plant_Type"

tree_diam = "Tree_Diameter"
plant_diam = "Diameter"

# Add fields to their corresponding FieldMap objects.
fm_type.addInputField(in_file1, tree_type)
fm_type.addInputField(in_file2, plant_type)

fm_diam.addInputField(in_file1, tree_diam)
fm_diam.addInputField(in_file2, plant_diam)

# Set the output field properties for both FieldMap objects.
type_name = fm_type.outputField
type_name.name = 'Veg_Type'
fm_type.outputField = type_name

diam_name = fm_diam.outputField
diam_name.name = 'Veg_Diam'
fm_diam.outputField = diam_name

# Add the FieldMap objects to the FieldMappings object.
fms.addFieldMap(fm_type)
fms.addFieldMap(fm_diam)

# Merge the two feature classes.
arcpy.Merge_management([in_file1, in_file2], output_file, fms)

FieldMappings example 2

This sample displays the option of using FieldMap objects to merge fields, using the FeatureClassToFeatureClass tool. In this example, a feature class contains information about the number of accidents per intersection in a city. Each year of data is maintained in one field. The user would like to find the average number of accidents in each intersection, without altering the existing table.

# Import the arcpy module
import arcpy

# Set the workspace
arcpy.env.workspace = 'c:/base/data.gdb'

in_file = 'AccidentData'
out_file = 'AverageAccidents'

# Create the necessary FieldMap and FieldMappings objects.
fm = arcpy.FieldMap()
fm1 = arcpy.FieldMap()
fms = arcpy.FieldMappings()

# Each field with accident data begins with 'Yr' (from Yr2007 to Yr2012).
#   The next step loops through each of the fields beginning with 'Yr', and adds
#   them to the FieldMap Object.
for f in arcpy.ListFields(in_file, 'Yr*'):
    fm.addInputField(in_file, f.name)

# Set the merge rule to find the mean value of all fields in the FieldMap object.
fm.mergeRule = 'Mean'

# Set properties of the output name.
f_name = fm.outputField
f_name.name = 'AvgAccidents'
f_name.aliasName = 'AvgAccidents'
fm.outputField = f_name

# Add the intersection field to the second FieldMap object.
fm1.addInputField(in_file, "Intersection")

# Add both FieldMaps to the FieldMappings Object
fms.addFieldMap(fm)
fms.addFieldMap(fm1)

# Create the output feature class, using the FieldMappings object.
arcpy.FeatureClassToFeatureClass_conversion(in_file, arcpy.env.workspace,
                                            out_file, "", fms)