Hfrhyu

I want to merge shapefiles after selection inside a loop and then save results to excel files. However, the codes could save the last result to excel files and can not save each merge file.

import arcpy
arcpy.env.workspace = "D:/STAR/GISpro.gdb"
arcpy.env.overwriteOutput = True #overwrite the exsiting files
selection1 = '"gridcode"<=14.3'
selection2 = '"gridcode">14.3 AND "gridcode"<=28.6'
selection3 = '"gridcode">28.6 AND "gridcode"<=42.9'
selection4 = '"gridcode">42.9 AND "gridcode"<=57.2'
selection5 = '"gridcode">57.2 AND "gridcode"<=71.5'
selection6 = '"gridcode">71.5 AND "gridcode"<=85.8'
selection7 = '"gridcode">85.8 AND "gridcode"<=100'

selections = [selection1, selection2, selection3, selection4,
 selection5, selection6, selection7]
layers = ["wqi_Conshp_clip27171","wqi_south8shp_clip27171"]

fc = "wqi_north8shp_clip27171" 

list = [] 

rows = arcpy.SearchCursor(fc) 
for row in rows: 
pop = row.getValue("Shape_Area") 
list.append(pop) 

Sum_Area27171 = sum(list)

for layer in layers:

arcpy.MakeFeatureLayer_management(layer,layer)

count = 0
statisticstables = []
selectionmerge = layer + "_Merge" # UPDATE THIS

for selection in selections:
 count = count + 1
 selectionname = layer + "level" + str(count)

 statisticstables.append(selectionname)
 arcpy.SelectLayerByAttribute_management(layer,'NEW_SELECTION',selection)
 arcpy.Statistics_analysis(layer,selectionname,[["Shape_Area","sum"]])
 arcpy.AddField_management(selectionname,'rate','DOUBLE')
 arcpy.CalculateField_management(selectionname,'rate','!SUM_Shape_Area!/'.format(Sum_Area27171),'PYTHON_9.3') 
 print selectionname

try:
arcpy.Merge_management(statisticstables, selectionmerge) #move this line out of the loop. 
print selectionmerge
except ExecuteError as e:
print(e)
print(arcpy.GetMessages())

outpath = "D:\STAR\info_data_test_results"
outresult = outpath + "\" + layer + "_Merge" + ".xls"
arcpy.TableToExcel_conversion(selectionmerge,outresult) 

As you can see, I use "merge_management" to merge all results from selection loop but could just save the last result as an excel file. Could anyone provide some suggestions about this problem?

This is somewhat guessing since your code snippet doesn't include some of the details, however: it looks like you may be trying to merge a dataset with a dataset that doesn't exist already. The first time you go through the loop, the table you've named "selecationmerge" doesn't exist; in fact it's assigned to an empty string. Additionally it's awkward (and, likely slower) to repeatedly merge.

Two options:

1. build a list of the tables to merge and then merge all at once


2. Append the second (and subsequent) tables after the first table is created. Note that this would change the input layer, so if you want to keep the output separate initially it's not the best option.

Modifying your code from the question for the first option (merge after loop is finished):

# set your environment settings if you haven't done so already
arcpy.env.workspace = r"path_to_workspace"
count = 0
statisticstables = []
selectionmerge = r"path_to_output_table" # UPDATE THIS
for selection in selections:
 count = count + 1
 selectionname = "stats27171wqi_Conlevel" + str(count)
 print selectionname
 statisticstables.append(selectionname)
 arcpy.SelectLayerByAttribute_management('wqi_Conshp_clip27171','NEW_SELECTION',selection)
 arcpy.Statistics_analysis('wqi_Conshp_clip27171',selectionname,[["Shape_Area","sum"]])
 arcpy.AddField_management(selectionname,'rate','DOUBLE')
 arcpy.CalculateField_management(selectionname,'rate','!SUM_Shape_Area!/'.format(Sum_Area27171),'PYTHON_9.3') 

try:
 arcpy.Merge_management(statisticstables, selectionmerge) #move this line out of the loop. 
 print(arcpy.GetMessages())
except ExecuteError as e:
 print(e)
 print(arcpy.GetMessages())

Additional resources:

Merge: http://desktop.arcgis.com/en/arcmap/10.3/tools/data-management-toolbox/merge.htm#GUID-7D7965A6-8486-4AF1-AAFD-C0168DFD1124

Append: http://desktop.arcgis.com/en/arcmap/10.3/tools/data-management-toolbox/append.htm#C_GUID-FA9BFB50-2B63-4355-929C-E22B915A9103