Zusammenfassung
The FieldMap object provides a field definition and a list of input fields taken from a set of tables or feature classes.
Diskussion
The properties of the FieldMap object include the start and end position of an input text value, so an output value can be created using a slice of an input value. If a FieldMap object contains multiple input fields from the same table or feature class, each record's values are merged using the mergeRule property. This is a convenient way to join values, such as a street name that is held in one field and a street type that is held in another, for example, Eureka and Street. The joinDelimiter property of the FieldMap object is used when Join is specified as the mergeRule value. Any set of characters, such as a space, can be used as a delimiter. In the example above, this would create a value of Eureka Street.
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. The easiest way to work with these objects is to first create a FieldMappings object, then initialize its FieldMap objects by adding the input feature classes or tables that are to be combined. Once all inputs are provided, the FieldMappings object will contain one FieldMap object, or output field, for each unique field name from all the inputs. You can modify this list by adding new fields, altering the properties or contents of an output field, or removing unwanted output fields.
Syntax
FieldMap ()
Eigenschaften
| Eigenschaft | Erläuterung | Datentyp |
| inputFieldCount (Schreibgeschützt) | The number of defined input fields. | Integer |
| joinDelimiter (Lesen und schreiben) | A string value used to separate input values from the same table if the output field type is string and the mergeRule is Join. | String |
| mergeRule (Lesen und schreiben) | Defines how values from two or more fields from the same input table are merged into a single output value. Valid choices are as follows:
| String |
| outputField (Lesen und schreiben) | The properties of the output field are either set or returned in a Field object. | Field |
Methodenübersicht
| Methode | Erläuterung |
| addInputField (table_dataset, field_name, {start_position}, {end_position}) | Adds input field to the field map. |
| findInputFieldIndex (table_dataset, field_name) | Finds an input field from the field map. |
| getEndTextPosition (index) | Returns the end text position from the field map. |
| getInputFieldName (index) | Returns the name of an input field from the field map, based on the field's index position. |
| getInputTableName (index) | Returns the name of an input table from the field map, based on the table's index position. |
| getStartTextPosition (index) | Returns the start text position from the FieldMap object. |
| removeAll () | Removes all values and creates an empty object. |
| removeInputField (index) | Removes an input field from the FieldMap object. |
| setEndTextPosition (index, end_position) | Sets end text position for the field map. |
| setStartTextPosition (index, start_position) | Sets the start text position from the field map. |
Methoden
addInputField (table_dataset, field_name, {start_position}, {end_position})| Parameter | Erläuterung | Datentyp |
table_dataset | The table added to the field map. | String |
field_name | The input field name. | String |
start_position | The start position of an input text value. (Der Standardwert ist -1) | Integer |
end_position | The end position of an input text value. (Der Standardwert ist -1) | Integer |
findInputFieldIndex (table_dataset, field_name)
| Parameter | Erläuterung | Datentyp |
table_dataset | The table added to the field map. | String |
field_name | The field name. | String |
| Datentyp | Erläuterung |
| Integer | The index position of the field name. |
getEndTextPosition (index)
| Parameter | Erläuterung | Datentyp |
index | The index position. | Integer |
| Datentyp | Erläuterung |
| Integer | The end text position. |
getInputFieldName (index)
| Parameter | Erläuterung | Datentyp |
index | The index position. | Integer |
| Datentyp | Erläuterung |
| String | The input field name. |
getInputTableName (index)
| Parameter | Erläuterung | Datentyp |
index | The index position. | Integer |
| Datentyp | Erläuterung |
| String | The input table name. |
getStartTextPosition (index)
| Parameter | Erläuterung | Datentyp |
index | The index position. | Integer |
| Datentyp | Erläuterung |
| Integer | The start text position. |
removeAll ()
removeInputField (index)
| Parameter | Erläuterung | Datentyp |
index | The index position. | Integer |
setEndTextPosition (index, end_position)
| Parameter | Erläuterung | Datentyp |
index | The index position. | Integer |
end_position | The end position of an input text value. | Integer |
setStartTextPosition (index, start_position)
| Parameter | Erläuterung | Datentyp |
index | The index position. | Integer |
start_position | The start position of an input text value. | Integer |
Codebeispiel
FieldMap objects are often used to merge similar datasets into one, all-encompassing dataset. In this example, the Trees feature class and the Plants.shp shapefile 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 arcpy
# Set the workspace
arcpy.env.workspace = 'c:/base'
in_features_1 = 'data.gdb/Trees'
in_features_2 = 'Plants.shp'
out_features = '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_features_1, tree_type)
fm_type.addInputField(in_features_2, plant_type)
fm_diam.addInputField(in_features_1, tree_diam)
fm_diam.addInputField(in_features_2, plant_diam)
# Set the output field properties for both FieldMap objects.
type_field = fm_type.outputField
type_field.name = 'Veg_Type'
fm_type.outputField = type_field
diam_field = fm_diam.outputField
diam_field.name = 'Veg_Diam'
fm_diam.outputField = diam_field
# Add the FieldMap objects to the FieldMappings object.
fms.addFieldMap(fm_type)
fms.addFieldMap(fm_diam)
# Merge the two feature classes.
arcpy.management.Merge([in_features_1, in_features_2], out_features, fms)This sample illustrates using FieldMap objects to merge fields using the ExportFeatures 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 wants to find the average number of accidents in each intersection without altering the existing table.
import arcpy
in_features = r'c:/base/data.gdb/AccidentData'
out_features = r'c:/base/data.gdb/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'.
# The next step loops through each of the fields beginning with 'Yr',
# and adds them to the FieldMap object.
for field in arcpy.ListFields(in_features, 'Yr*'):
fm.addInputField(in_features, field.name)
# Set the merge rule to find the mean value of all fields in the
# FieldMap object.
fm.mergeRule = 'Mean'
# Set the properties of the output field.
out_field = fm.outputField
out_field.name = 'AvgAccidents'
out_field.aliasName = 'AvgAccidents'
fm.outputField = out_field
# Add the intersection field to the second FieldMap object.
fm1.addInputField(in_features, "Intersection")
# Add both FieldMap objects to the FieldMappings object.
fms.addFieldMap(fm)
fms.addFieldMap(fm1)
# Create the output feature class using the FieldMappings object.
arcpy.conversion.ExportFeatures(in_features, out_features, field_mapping=fms)