Use Value Tables in Python as part of a Geoprocessing script

Summary

A Value Table is a flexible object that can be used as input for a multivalue parameter. A number of GP tools can optionally use Value Tables. For example, Union, Merge or any tool that has a multivalue parameter.

Procedure

• Below is an example of the Merge command NOT using a Value Table:
  
  

  Code:
  # Import system modules
  import sys, string, os, win32com.client
  
  # Create the Geoprocessor object
  gp = win32com.client.Dispatch("esriGeoprocessing.GpDispatch.1")
  
  # Load required toolboxes...
  gp.AddToolbox("C:/Program Files/ArcGIS/ArcToolbox/Toolboxes/Data Management Tools.tbx")
  
  # Process: Merge...
  gp.Merge_management("C:\\ESRI\\ESRIDATA\\MEX_STATES.shp;C:\\ESRI\\ESRIDATA\\USA_STATES.shp",
                      "C:\\ESRI\\ESRIDATA\\STATES_Merge.shp")
  
  print "done"

  
  This example uses the text value of the multivalue parameter, which can become difficult to use when there are numerous values with complex paths. The Value Table is used to organize the values into a table, so values can be easily added or removed, eliminating the complexity of parsing a multivalue text string. Below is an example using Merge with a Value Table:
  
  

  Code:
  # Import system modules
  import sys, string, os, win32com.client
  
  # Create the Geoprocessor object
  gp = win32com.client.Dispatch("esriGeoprocessing.GpDispatch.1")
  
  # Set the workspace. 
  gp.Workspace = "C:\\ESRI\\ESRIDATA\\"
  
  # Merge shape type, input Polyline or Polygon
  shapeType = "Polygon"
  
  gp.OverwriteOutput = 1
  
  # Create the value table
  vtab = gp.CreateObject("ValueTable")
  
  # List all of the feature classes in the dataset
  fcs = gp.ListFeatureClasses()
  fcs.reset()
  fc = fcs.next()
  
  # Store all the feature classes in a value table
  while fc:
      # Describe the feature class
      dsc = gp.Describe(fc)
      if dsc.Shapetype == shapeType:
          vtab.AddRow(fc)
      fc = fcs.next()
  
  # Process: Merge...
  gp.Merge_management(vtab, "C:\\ESRI\\ESRIDATA\\STATES_Merge.shp")
  
  print "done"

  
  
• Value Tables can have many fields. In the examples above, a Value Table of one column is created. This is the default:
  
  

  Code:
  vtab = gp.CreateObject("ValueTable")

  
  Some tools accept Value Tables with multiple columns. For example, the Union_analysis tool accepts in a two column value table consistening of input feature classes and ranks. When populating a Value Table with multiple columns, the column seperator is a space:
  
  

  Code:
  # Import system modules
  import sys, string, os, win32com.client
  
  # Create the Geoprocessor object
  gp = win32com.client.Dispatch("esriGeoprocessing.GpDispatch.1")
  
  # Create the value table for the Analysis Union tool with 2 columns
  vtab = gp.CreateObject("ValueTable", 2)
  
  # Set the workspace. 
  gp.Workspace = "C:\\ESRI\\ESRIDATA\\"
  
  gp.OverwriteOutput = 1
  
  # List all of the feature classes in the dataset
  fcs = gp.ListFeatureClasses()
  fcs.reset()
  fc = fcs.next()
  
  while fc: 
      # Update the value table with a rank of 2 for each record, except MEX_STATES
      if fc <> "MEX_STATES":
         vtab.AddRow(fc + " " + "2")
      else:
         vtab.AddRow(fc + " " + "1")
      fc = fcs.next()   
  
  # Union the feature classes
  gp.Union_analysis(vtab, "union_out")
  
  print "done"

  
  However, there may be times when the values put in the Value Table themselves may have spaces. For example paths or shapefiles with spaces in the name. It is therefore good practise to put each value in single quotes. For example:
  
  

  Code:
  # Import system modules
  import sys, string, os, win32com.client
  
  # Create the Geoprocessor object
  gp = win32com.client.Dispatch("esriGeoprocessing.GpDispatch.1")
  
  # Create the value table for the Analysis Union tool with 2 columns
  vtab = gp.CreateObject("ValueTable", 2)
  
  # Set the workspace. 
  gp.Workspace = "C:\\ESRI\\ESRIDATA\\"
  
  gp.OverwriteOutput = 1
  
  # List all of the feature classes in the dataset
  fcs = gp.ListFeatureClasses()
  fcs.reset()
  fc = fcs.next()
  
  while fc: 
      # Update the value table with a rank of 2 for each record, except rivers
      if fc <> "MEX_STATES":
         vtab.AddRow("'" + fc + "'" + " " + "'2'")
      else:
         vtab.AddRow("'" + fc + "'" + " " + "'1'")
      fc = fcs.next()   
  
  # Union the feature classes
  gp.Union_analysis(vtab, "union_out")
  
  print "done"

  
  
• Value Tables can also be used as a convenient array object, similar to a VB Array. For example:
  
  

  Code:
  # Import system modules
  import sys, string, os, win32com.client
  
  # Create the Geoprocessor object
  gp = win32com.client.Dispatch("esriGeoprocessing.GpDispatch.1")
  
  size = 2
  
  # Populate the Value Table with some values
  vt = gp.CreateObject("ValueTable", size)
  vt.SetRow(0, "'E' 'S'")
  vt.SetRow(1, "'R' 'I'")
  
  # Read the Value Table
  for i in range(vt.rowcount):
      for j in range(vt.columncount):
          print vt.getvalue(i, j)