Resumen
The FieldMap object provides a field definition and a list of input fields taken from a set of tables or feature classes.
Debate
El objeto FieldMappings es una colección de objetos FieldMap y se utiliza como valor de parámetro para las herramientas que realizan la asignación de campos, tales como Merge. La manera más fácil de trabajar con estos objetos es crear primero un objeto FieldMappings y, a continuación, inicializar sus objetos FieldMap agregando las clases de entidad o las tablas de entrada que se vayan a combinar. Una vez proporcionadas todas las entradas, el objeto FieldMappings contendrá un objeto FieldMap, o campo de salida, para cada nombre de campo único de todas las entradas. Esta lista se puede modificar agregando nuevos campos, modificando las propiedades o los contenidos de un campo de salida, o quitando los campos de salida no deseados.
Las propiedades del objeto FieldMap incluyen la posición de inicio y final de un valor de texto de entrada, de modo que se pueda crear un nuevo valor de salida utilizando una sección de un valor de entrada. Si un objeto FieldMap contiene varios campos de entrada de la misma tabla o clase de entidad, los valores de cada registro se combinan utilizando la propiedad mergeRule. Ésta es una manera conveniente de unir valores, tales como un nombre de calle contenido en un campo y un tipo de calle contenido en otro, por ejemplo, Eureka y Street. La propiedad joinDelimiter de FieldMap si se utiliza si se especifica el valor de mergeRule Join. Cualquier conjunto de caracteres, tal como un espacio, se puede utilizar como delimitador. En el ejemplo anterior, esto crearía el valor Eureka Street.
Sintaxis
FieldMap ()
Propiedades
Propiedad | Explicación | Tipo de datos |
inputFieldCount (Sólo lectura) | The number of defined input fields. | Integer |
joinDelimiter (Lectura y escritura) | 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 (Lectura y escritura) | 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 (Lectura y escritura) | The properties of the output field are either set or returned in a Field object. | Field |
Vista general del método
Método | Explicación |
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) | Gets end text position from the field map. |
getInputFieldName (index) | Gets the name of an input field from the field map, based on the field's index. |
getInputTableName (index) | Gets the name of an input table from the field map, based on the table's index. |
getStartTextPosition (index) | Gets start text position from the field map. |
removeAll () | Removes all values and creates an empty object. |
removeInputField (index) | Removes an input field from the field map. |
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. |
Métodos
addInputField (table_dataset, field_name, {start_position}, {end_position})
Parámetro | Explicación | Tipo de datos |
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. (El valor predeterminado es -1) | Integer |
end_position | The end position of an input text value. (El valor predeterminado es -1) | Integer |
findInputFieldIndex (table_dataset, field_name)
Parámetro | Explicación | Tipo de datos |
table_dataset | The table added to the field map. | String |
field_name | The field name. | String |
Valor de retorno
Tipo de datos | Explicación |
Integer | The index position of the field name. |
getEndTextPosition (index)
Parámetro | Explicación | Tipo de datos |
index | The index position. | Integer |
Valor de retorno
Tipo de datos | Explicación |
Integer | The end text position. |
getInputFieldName (index)
Parámetro | Explicación | Tipo de datos |
index | The index position. | Integer |
Valor de retorno
Tipo de datos | Explicación |
String | The input field name. |
getInputTableName (index)
Parámetro | Explicación | Tipo de datos |
index | The index position. | Integer |
Valor de retorno
Tipo de datos | Explicación |
String | The input table name. |
getStartTextPosition (index)
Parámetro | Explicación | Tipo de datos |
index | The index position. | Integer |
Valor de retorno
Tipo de datos | Explicación |
Integer | The start text position. |
removeAll ()
removeInputField (index)
Parámetro | Explicación | Tipo de datos |
index | The index position. | Integer |
setEndTextPosition (index, end_position)
Parámetro | Explicación | Tipo de datos |
index | The index position. | Integer |
end_position | The end position of an input text value. | Integer |
setStartTextPosition (index, start_position)
Parámetro | Explicación | Tipo de datos |
index | The index position. | Integer |
start_position | The start position of an input text value. | Integer |
Muestra de código
FieldMap 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 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)
FieldMap 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 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 field in arcpy.ListFields(in_file, 'Yr*'):
fm.addInputField(in_file, field.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, field_mapping=fms)