Latest Contributions by HOWARDWILLIAMS

Thank you to all who responded to this question earlier.  I am re-posting a more specific question and hopefully my code will be easier to understand. So, I have number of feature classes in a .gdb that have tree counts per acre in each polygon by year.  I am iteratively unioning the features by year adding a field that is the sum of the previous tree count with the new tree count. import arcpy arcpy.CheckOutExtension("spatial") arcpy.env.overwriteOutput=True arcpy.env.workspace="C:\LPP\APS.gdb" R1="R1ADS" Dam="Damage" years=['1999','2000', '2001', '2002', '2003', '2004', '2005', '2006', '2007', '2008', '2009', '2010', '2011', '2012', '2013'] fields=['TPA_','Acres_','NoTrees_'] ###R1+years(i)+Dam is the name of the feature in the .gdb that will be unioned RangeYear=['1999_2000','1999_2001','1999_2002','1999_2003','1999_2004','1999_2005', '1999_2006','1999_2007','1999_2008','1999_2009','1999_2010','1999_2011','1999_2012','1999_2013'] ### RangeYear is a variable that I created for naming the unioned outfeature #________________________________________________ ###The statement below create first RangeYear feature to base iteration on in following loop.  Because only two years are being added it requires a simple Field Calculator Expression to sum the trees per acre per year which I was able to figure out. arcpy.Union_analysis([R1+years[0]+Dam,R1+years[1]+Dam],R1+years[0]+"_"+years[1]+Dam) for j in range(0,3):     arcpy.AddField_management(R1+years[0]+"_"+years[1]+Dam,fields +RangeYear[0],"FLOAT","","","") ###I tried to but the statements below in the loop above by having the Field Calculator expressions in a list also, however ###the program would not allow me to iterate through that list so I plugged the expression into the parameters below and ran the tool one at a ###time. arcpy.CalculateField_management(R1+years[0]+"_"+years[1]+Dam,fields[0]+RangeYear[0],'!TPA_1999!+!TPA_2000!',"PYTHON") arcpy.CalculateField_management(R1+years[0]+'_'+years[1]+Dam,fields[0]+RangeYear[0],'!Shape_Area! * 0.00024710538',"PYTHON") arcpy.CalculateField_management(R1+years[0]+'_'+years[1]+Dam,fields[0]+RangeYear[0],'!TPA_1999_2000!*!Acres_1999_2000!',"PYTHON") ###The loop below unions the remaining years the previous years with the next chronological year; ###adds three new field; calculates the new fields values and then move on to the next union. for i in range(0,13) :       arcpy.Union_analysis([R1+years[0]+"_"+years[i+1]+Dam,R1+years[i+2]+Dam],R1+years[0]+"_"+years[i+2]+Dam)              for j in range(0,3):                   arcpy.AddField_management(R1+years[0]+'_'+years[i+2]+Dam,fields +RangeYear[i+1],"FLOAT","","","")                   arcpy.CalculateField_management(R1+years[0]+'_'+years[i+2]+Dam,fields , ????Expression????, "PYTHON")     ###OK so the major crux here is that for TPA_1999_20XX, I need to add the previously unioned TPA_1999_20XX-1 to TPA_20XX. ###I have no idea how to do this.  I suspect that once I figure this out, the next two expressions will be evident. ####################################Thanks for reading, sorry for being such a hack programmer!#################### Field Calculator Expression Arcpy Message was edited by: HOWARD WILLIAMS ... View more

So I am writing a script to perform a Union on multiple feature data sets.  Feature data sets:  R1ADS1999Damage, R1ADS2000Damage.....R1ADS2013Damage  (these are all polygon feature classes with the same attribute fields years 1999-2013) I need to join the first (1999) year to the next year, naming the joined feature class R1ADS1999-2000Damage, and then add three new fields called: TPA_1999_2000; Acres_1999_2000 and; NoTrees_1999_2000.  Each new field is calculated with a unique (field calculator) expression.  I will provide these calculations in a moment.  Once the fields are added and the values calculated the newly created unioned feature class, R1ADS1999-2000Damage, needs to be unioned to R1ADS2001Damage, the next chronological year. Fields called  TPA_1999_2001; Acres_1999_2001 and; NoTrees_1999_2001  need to be added and calculated.  This pattern continues until the final year 2013. TPA_1999_2000 = Is the sum of field TPA_1999 + TPA_2000, after the next union the TPA_1999_2001= TPA_1999_2000+TPA_2001 this pattern continues for after all unions. Acres_1999_2000= Is a recalculation of geometry after the union, in Acres. This is the same for all subsequent unions. No_Trees_1999_2000= Is TPA_1999_2000 * Acres_1999_2000. After the next union the NoTrees_1999_2001= TPA_1999_2001*Acres1999_2001 I have managed to get the union and adding fields part of the script done, see below.  I got stuck on writing the Field Calculator expression for the TPA_1999_20XX.  It seems that I need an expression that sums all of the fields that begin with TPA_  something like TPA_1999_2000= sum([!TPA_*!)   However this does not work.  So here is the code I have come up with so far until got stuck: ################################################## R1="R1ADS" Dam="Damage" years=['1999','2000', '2001', '2002', '2003', '2004', '2005', '2006', '2007', '2008', '2009', '2010', '2011', '2012', '2013'] fields=['TPA_','Acres_','NoTrees_'] RangeYear= ['1999_2000','1999_2001','1999_2002','1999_2003','1999_2004','1999_2005','1999_2006','1999_2007','1999_2008','1999_2009','1999_2010','1999_2011','1999_2012','1999_2013'] expression=['TPA_ expression', 'Acres_expression', 'NoTree_expession'] ### Note these are place holders for the correct expressions that I need help with. arcpy.Union_analysis([R1+years[0]+Dam,R1+years[1]+Dam],R1+years[0]+"_"+years[1]+Dam) for i in range(0,13) :   arcpy.Union_analysis([R1+years[0]+"_"+years[i+1]+Dam,R1+years[i+2]+Dam],R1+years[0]+"_"+years[i+2]+Dam)   print years[0]+'_'+years[i+2]+" union done"          for j in range(0,3):                  arcpy.AddField_management(R1+years[0]+'_'+years[i+2]+Dam, fields +RangeYear, "FLOAT","","","")                  arcpy.CalculateField_Management(R1+years[0]+'_'+years[i+2]+Dam, fields +RangeYear,expression ) I would appreciate any help you can give, please do not worry about insulting me I am new to programming. Thanks ... View more