Merging rasters from multiple days in loop using ArcPy

Question

I'm using ArcGIS Pro 2.9.3, and I want to use the Mosaic to New Raster tool to merge groups of rasters. I have many days that each have multiple rasters within them. For example, I have

July3a.tif

July3b.tif

July3c.tif

July10a.tif

July10b.tif

July10c.tif

July11a.tif

July11b.tif

July11c.tif

So in this case, I'd want to merge July3a.tif-July3c.tif into one raster, July3.tif, then July10a.tif-July10c.tif into July10.tif, and so on.

I've scratched out a basic while loop, but it only works for one day at a time, and it would be awfully time consuming to adjust the arguments for each and every day.

i = July3a.tif
while i = July3*.tif
arcpy.management.MosaicToNewRaster(i, output_location, July3.tif, {coordinate_system_for_the_raster}, {pixel_type}, {cellsize}, number_of_bands, {mosaic_method}, {mosaic_colormap_mode})
i += 1

Is it possible to make a loop that merges multiple days at once?

• Hornbydd: For each day do you only ever have the a, b and c versions or do they randomly go to z?
• Beck: @Hornbydd The latter. My rasters are satellite images that have been filtered for clouds, so some dates have more or less images than others.

Answer 1

Here is the code you can use, obviously I don't have your data so I spoofed it up with text files, so you need to edit the code and replace the txt with tif.

Here is my sample data:

Spoofed data

# Import modules
import arcpy
import glob
import os
import collections
# Read tiff files in folder into a list
folder = r"C:\temp"
lstTIFFS = glob.glob(folder + r"\*.txt") # replace txt with tif
# Create special dictionary where the items will be inserted into a set
dicFiles = collections.defaultdict(set)
# Build dictionary, key is day and item is a set of characters, e.g. june6,{a,b,c}
for fp in lstTIFFS:
 fn = os.path.basename(fp)[:-4]
 character = fn[-1] # returns something like a
 day = fn[:-1] # returns something like june6
 dicFiles[day].add(character)
# Mosaic data for each day
for k,v in dicFiles.iteritems():
 # create empty list of files for a single day
 lstInputs = list()
 # Build full path and insert into list
 for character in v:
 fp = folder + "\\" + k + character + ".txt"
 lstInputs.append(fp)
 # Mosaic data
 outputname = "Merged_" + k + ".tif"
 arcpy.MosaicToNewRaster_management(lstInputs,r"C:\temp",outputname) # Important! set other parameters

This code is developed for ArcMap so if you want to run it in ArcGIS Pro you need to change this line:

for k,v in dicFiles.iteritems():

to

for k,v in dicFiles.items():