[ncl-talk] Problems with averaging over a do loop

Fri Jun 5 12:11:58 MDT 2015

For the FillValue though, here is my question. Let's say point 2,2 (whatever lat,lon that is) is -9999 in one file but 5.0 in the other, what value will it be given when using the average? I don't want it to show 5, it should show 2.5.

-----Original Message-----
From: ncl-talk-bounces at ucar.edu [mailto:ncl-talk-bounces at ucar.edu] On Behalf Of Walter Kolczynski
Sent: Friday, June 05, 2015 1:08 PM
To: ncl-talk at ucar.edu
Subject: Re: [ncl-talk] Problems with averaging over a do loop

One more I just saw: 

5) You are assigning AODVIS at _FillValue, and then immediately deleting it. (a) This is pointless, (b) You should only need to assign the fill value if the value assigned when the grib is read is incorrect for some reason (rare), (c) zero is generally not used as a fill value (remember that anything equal to the fill value will be treated as missing and ignored in most NCL computations).

- Walter

On 05-Jun-15 13:56, Walter Kolczynski wrote:

	Steven,

	Several things:

	1) You didn't create the AODSum array with two dimensions, you created an array with one dimension of length 2 (check your printVarSummary). To create a multi-dimensional array with new you need to pass in an array of the dimension sizes.
	2) NCL has functions to average over a specified dimension. You should read all of your files in at once with a[:]->VAR_147_GDS0_EATM and then use dim_avg_n_Wrap to average. This will both be cleaner (no need for an AODSum at all) and eliminate the do loop (which are slow in interpreted languages such as NCL).
	3) Since you want to create a new record dimension when reading in the variables, you should be using "join" mode instead of the default "cat" for your file list by calling ListSetType(a, "join").
	4) Because you are reading in LAT and LON across all files, you are creating an array that has multiple copies of the lat/lon arrays, which is likely not what you want. Since lat/lon do not change, you should just read them from the first file in the array (a[0]), plus...
	4a) You do not need to assign LAT and LON as attributes of AODVIS. They are already coordinates for the appropriate dimensions of AODVIS.

	- Walter

	On 05-Jun-15 12:15, BLIUJUS, STEVEN D CTR USAF AFMC AFLCMC/HBAW-OL wrote:

		I am trying to take an average of a value in several files. The values are
		an array. In this case the Variable is AOD which is based on Lat/Lon. I can
		manually sum them and create and average, but I am trying to create a do
		loop such that if I have several files (40) I can average that value. All
		files have the exact same lat/lon, just the AOD value is different. I have
		attached two scripts. The first one is gribtest.ncl. This script is where I
		manually add the two files. The other attached is AOD.ncl. This is where I
		am trying to create a do loop. I am trying to create an empty array before
		the do loop called AODSum. However, when the loop executes I dies when
		trying to add with the message:

		fatal:Plus: Number of dimensions do not match, can't continue
		fatal:["Execute.c":8128]:Execute: Error occurred at or near line 37 in file
		AOD.ncl

		(0)     Error: scalar_field: If the input data is 1-dimensional, you must
		set sfXArray and sfYArray to 1-dimensional arrays of the same length.
		warning:create: Bad HLU id passed to create, ignoring it

		I created the array with two dimensions so I am not sure why it is failing.
		The two files are much too large to send via email, so if those need to be
		viewed I'd have to send them another way. Here is all the variable summaries
		though:

		Variable: LAT
		Type: float
		Total Size: 2888 bytes
		            722 values
		Number of Dimensions: 1
		Dimensions and sizes:   [g0_lat_1 | 722]
		Coordinates:
		            g0_lat_1: [-90..90]
		Number Of Attributes: 9
		  long_name :   latitude
		  GridType :    Cylindrical Equidistant Projection Grid
		  units :       degrees_north
		  Dj :  0.5
		  Di :  0.5006954
		  Lo2 : 360
		  La2 : 90
		  Lo1 :  0
		  La1 : -90

		Variable: LON
		Type: float
		Total Size: 5760 bytes
		            1440 values
		Number of Dimensions: 1
		Dimensions and sizes:   [g0_lon_2 | 1440]
		Coordinates:
		            g0_lon_2: [ 0..360]
		Number Of Attributes: 9
		  long_name :   longitude
		  GridType :    Cylindrical Equidistant Projection Grid
		  units :       degrees_east
		  Dj :  0.5
		  Di :  0.5006954
		  Lo2 : 360
		  La2 : 90
		  Lo1 :  0
		  La1 : -90

		Variable: AODSum
		Type: float
		Total Size: 8 bytes
		            2 values
		Number of Dimensions: 1
		Dimensions and sizes:   [2]
		Coordinates:
		Number Of Attributes: 1
		  _FillValue :  9.96921e+36

		Variable: AODVIS
		Type: float
		Total Size: 1039680 bytes
		            259920 values
		Number of Dimensions: 2
		Dimensions and sizes:   [g0_lat_1 | 361] x [g0_lon_2 | 720]
		Coordinates:
		            g0_lat_1: [-90..90]
		            g0_lon_2: [ 0..360]
		Number Of Attributes: 15
		  LON : <ARRAY of 1440 elements>
		  LAT : <ARRAY of 722 elements>
		  sub_center :  Ocean Prediction Center
		  center :      U.S. Air Force - Global Weather Center
		  long_name :   Unknown Variable Name
		  units :       unknown
		  _FillValue :  1e+20
		  level_indicator :     200
		  gds_grid_type :       0
		  parameter_table_version :     129
		  parameter_number :    147
		  level :       0
		  forecast_time :       0
		  forecast_time_units : hours
		  initial_time :        07/20/2010 (00:00)

		Steven Bliujus, Contractor
		SEMS/16WS WXE
		557th Weather Wing
		DNS: 232-7151

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	-- 
	Walter Kolczynski, Jr.
	Global Ensemble Team
	NOAA/NWS/NCEP/EMC (via I.M. Systems Group)
	(301) 683-3781

-- 
Walter Kolczynski, Jr.
Global Ensemble Team
NOAA/NWS/NCEP/EMC (via I.M. Systems Group)
(301) 683-3781