ArcGIS Help 10.2 - FieldMappings (arcpy)

摘要

FieldMappings 对象是一组 FieldMap 对象，用作制图工具的参数值，例如“合并”。

讨论

FieldMappings 对象是一组 FieldMap 对象，它用作执行字段映射的工具的参数值，如 Merge。要处理这些对象，最简单的方法就是先创建 FieldMappings 对象，然后通过添加要组合的输入要素类或表对 FieldMap 对象进行初始化。提供了所有输入后，FieldMappings 对象将为所有输入中的每个唯一字段名提供一个 FieldMap 对象或输出字段。可对此列表进行修改，具体方法有添加新字段、更改输出字段的属性和/或内容，或移除任何不需要的输出字段。

FieldMap 对象的属性包括输入文本值的起始位置和结束位置，因此可以使用一组输入值创建新的输出值。如果 FieldMap 对象包含多个来自同一表或要素类的输入字段，则将使用 mergeRule 属性合并每个记录的值。这样可以方便地连接各个值，例如保存在一个字段中的街道名称以及保存在另一个字段中的街道类型，如 Eureka 和 Street。如果将 mergeRule 的值指定为 Join，则使用 FieldMap 的 joinDelimiter 属性。任何字符集（如空格）都可用作分隔符。在以上示例中，将会创建值 Eureka Street。

语法

FieldMappings ()

属性

属性	说明	数据类型
fieldCount (只读)	The number of output fields.	Integer
fieldMappings (读写)	A list of FieldMap objects that make up the FieldMappings object.	FieldMap
fieldValidationWorkspace (读写)	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 (只读)	A list of Field objects. Each field object represents the properties of each output field.	Field

方法概述

方法	说明
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.

方法

addFieldMap (field_map)

参数	说明	数据类型
field_map	The field map to add to the field mappings	FieldMap

addTable (table_dataset)

参数	说明	数据类型
table_dataset	The table to add to the field mappings object.	String

exportToString ()

返回值

数据类型	说明
String	The string representation of the object.

findFieldMapIndex (field_map_name)

参数	说明	数据类型
field_map_name	Find the field map by name.	String

返回值

数据类型	说明
Integer	The index position of the field map.

getFieldMap (index)

参数	说明	数据类型
index	The index position of the field map.	Integer

返回值

数据类型	说明
FieldMap	The field map from the field mappings.

loadFromString (string)

参数	说明	数据类型
string	The string representation of the object.	String

removeAll ()

removeFieldMap (index)

参数	说明	数据类型
index	The index position of the field map.	Integer

replaceFieldMap (index, value)

参数	说明	数据类型
index	The index position of the field map to be replaced.	Integer
value	The replacement field map.	FieldMap

代码实例

FieldMappings 示例

需要将相似数据集合并到一个无所不包的数据集中时，通常使用 FieldMap 对象。在该示例中，要素类 Trees 和 shapefile Plants.shp 合并至一个要素类：Vegetation。两个初始要素类均有两个属性：类型与直径。两个属性都必须通过合并进行维护。

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 示例 2

此示例使用 FeatureClassToFeatureClass 工具显示使用 FieldMap 对象合并字段的选项。在本示例中，要素类包含城市交叉点事故数量的信息。在一个字段中维护各年数据。用户想要在不更改现有表的情况下，查找各交叉点的平均事故数量。

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)

FieldMappings (arcpy)

摘要

讨论

语法

属性

方法概述

方法

代码实例

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