Desktop Help 10.0

Summary

The FieldMap object provides a field definition and a list of input fields taken from a set of tables or feature classes.

Discussion

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. This list can be modified by adding new fields, altering the properties and/or contents of an output field, or removing any unwanted output fields.

The properties of the FieldMap object include the start and end position of an input text value, so a new 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 FieldMap is used if the mergeRule value Join is specified. Any set of characters, such as a space, can be used as a delimiter. In the above example, this would create a value of Eureka Street.

Syntax

FieldMap ()

Properties

Property	Explanation	Data Type
inputFieldCount (Read Only)	Get the count of subfields.	Integer
joinDelimiter (Read and Write)	Join delimiter for the subfields.	String
mergeRule (Read and Write)	Merge rule for the subfields.	String
outputField (Read and Write)	Get the properties field.	Field

Method Overview

Method	Explanation
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.

Methods

addInputField (table_dataset, field_name, {start_position}, {end_position})

Parameter	Explanation	Data Type
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. (The default value is -1)	Integer
end_position	The end position of an input text value. (The default value is -1)	Integer

findInputFieldIndex (table_dataset, field_name)

Parameter	Explanation	Data Type
table_dataset	The table added to the field map.	String
field_name	The field name.	String

Return Value

Data Type	Explanation
Integer	The index position of the field name.

getEndTextPosition (index)

Parameter	Explanation	Data Type
index	The index position.	Integer

Return Value

Data Type	Explanation
Integer	The end text position.

getInputFieldName (index)

Parameter	Explanation	Data Type
index	The index position.	Integer

Return Value

Data Type	Explanation
String	The input field name.

getInputTableName (index)

Parameter	Explanation	Data Type
index	The index position.	Integer

Return Value

Data Type	Explanation
String	The input table name.

getStartTextPosition (index)

Parameter	Explanation	Data Type
index	The index position.	Integer

Return Value

Data Type	Explanation
Integer	The start text position.

removeAll ()

removeInputField (index)

Parameter	Explanation	Data Type
index	The index position.	Integer

setEndTextPosition (index, end_position)

Parameter	Explanation	Data Type
index	The index position.	Integer
end_position	The end position of an input text value.	Integer

setStartTextPosition (index, start_position)

Parameter	Explanation	Data Type
index	The index position.	Integer
start_position	The start position of an input text value.	Integer

Code Sample

FieldMap example

import arcpy
from arcpy import env

# Input feature classes contain a PID field that is a composite of
#   the Township, Range, Section, QuarterSection, Block, Lot, and SubLot values.
#   We need to define how to break the PID field into two fields: TWNSHIP and BLOCK,
#   then run the Merge tool.
#   PID field and field map. 
#                    1 1 1 1 1 1 1
#  1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
# +-------------------------------+
# |2|0|3|0|8|2|1|0|0|1|0|0|5|0|0|0|
# +-------------------------------+
# +---TWNSHIP---+-------BLOCK-----+

infc1 = "C:/Data/NewParcels.shp"
infc2 = "Parcels"
outfc = "Parcels_Merge"

# Create a fieldmappings object and two fieldmap objects
#
fieldmappings = arcpy.FieldMappings()
fldmap_TWNSHIP = arcpy.FieldMap()
fldmap_BLOCK = arcpy.FieldMap()

# Create a value table to hold names of input feature classes for Merge tool.
#
vt = arcpy.ValueTable()

# Add all fields from first input feature class to fieldmappings object
#   AddTable is the most efficient way.
#
fieldmappings.addTable(infc1)

# Add the TWNSHIP and BLOCK field from the first input feature class 
#   to fieldmap object.
#
fldmap_TWNSHIP.addInputField(infc1)
fldmap_BLOCK.addInputField(infc1)
vt.addRow(infc1)

# Add all fields from second input feature class to fieldmappings object
#
env.workspace = "C:/Data/Boulder.gdb"
fieldmappings.addTable(infc2)

# Add the TWNSHIP and BLOCK field from the second input feature class 
#   to fieldmap object.
#
fldmap_TWNSHIP.addInputField(infc2)
fldmap_BLOCK.addInputField(infc2)
vt.addRow(infc2)

# Set the starting and ending positions of the input field in the fieldmap.
#   This is for TWNSHIP
for x in range(0, fldmap_TWNSHIP.inputFieldCount):
    fldmap_TWNSHIP.setStartTextPosition(x, 0)
    fldmap_TWNSHIP.setEndFieldPosition(x, 6)

# Set the starting and ending positions of the input field in the fieldmap.
#   This is for BLOCK
for x in range(0, fldmap_BLOCK.inputFieldCount):
    fldmap_BLOCK.setStartTextPosition(x, 7)
    fldmap_BLOCK.setEndFieldPosition(x, 15)

# Get the new field object from fieldmap, set field name, place back in fieldmap.
#
fld_TWNSHIP = fldmap_TWNSHIP.outputField
fld_TWNSHIP.name = "TWNSHIP"
fldmap_TWNSHIP.outputField = fld_TWNSHIP
fld_BLOCK = fldmap_BLOCK.outputField
fld_BLOCK.name = "BLOCK"
fldmap_BLOCK.outputField = fld_BLOCK

# Add the new fieldmap object to fieldmappings object.
fieldmappings.addFieldMap(fldmap_TWNSHIP)
fieldmappings.addFieldMap(fldmap_BLOCK)

#Run the Merge tool
arcpy.Merge_management(vt, outfc, fieldmappings)

FieldMap

Summary

Discussion

Syntax

Properties

Method Overview

Methods

Code Sample

Related Topics