FieldMap (arcpy)

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: First —The first input value is used. Last —The last input value is used. Join —Merge the values together using the delimiter value to separate the values (only valid if the output field type is text). Min —The smallest input value is used (only valid if the output field type is numeric). Max —The largest input value is used (only valid if the output field type is numeric). Mean —The mean is calculated using the input values (only valid if the output field type is numeric). Median —The median is calculated using the input values (only valid if the output field type is numeric). Sum —The sum is calculated using the input values (only valid if the output field type is numeric). StDev —The standard deviation is calculated using the input values (only valid if the output field type is numeric). Count —The number of values included in statistical calculations. This counts each value except null values.	String
outputField (Lectura y escritura)	The properties of the output field are either set or returned in a Field object.	Field

Descripción general de los métodos

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

Ejemplo 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 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)

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 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)