topic Re: Round to nearest 100th in Python Questions

Round to nearest 100th

ChrisBrannin — Thu, 06 Jun 2013 14:57:40 GMT

I am a little confused about how to round a field to the nearest 100th. Would I use math.ceil() or the round()?

math.ceil([field]/100)*100

Does this only round down though?

Thanks

Re: Round to nearest 100th

MathewCoyle — Thu, 06 Jun 2013 15:05:25 GMT

math.ceil() always rounds up. math.floor() rounds down. round() rounds the the nearest integer or to a particular decimal place if the second parameter is specified.

round([field], 2)

Re: Round to nearest 100th

ChrisBrannin — Sat, 11 Dec 2021 20:14:00 GMT

I am a little confused about how to round a field to the nearest 100th. Would I use math.ceil() or the round()?
math.ceil([field]/100)*100
Does this only round down though?

Thanks

How I mean to phrase this question is, how to round a number (say 11) to 0 instead of 100?

Re: Round to nearest 100th

MathewCoyle — Thu, 06 Jun 2013 15:11:14 GMT

How I mean to phrase this question is, how to round a number (say 11) to 0 instead of 100?

You would use a negative number for the second round() parameter of course. Use int() to ensure it returns an integer instead of float.

int(round([field], -2))

Re: Round to nearest 100th

ChrisBrannin — Thu, 06 Jun 2013 15:17:06 GMT

You would use a negative number for the second round() parameter of course. Use int() to ensure it returns an integer instead of float.
int(round([field], -2))

That is the winner right there, thank you! I knew ther was a better way then to use math.ceil(). I really appreciate the help.

Re: Round to nearest 100th

ChrisBrannin — Sat, 11 Dec 2021 20:14:03 GMT

You would use a negative number for the second round() parameter of course. Use int() to ensure it returns an integer instead of float.
int(round([field], -2))

How can I use this outside of arcmap? When I try, an error of "Invalid field [field]" appears.

I am trying to use it like this:

rndValue = "int(round(!ELEVATION!, -2))"

...

arcpy.CalculateField_management(elev, fieldName, rndValue, "PYTHON")

Thank you

Re: Round to nearest 100th

MathewCoyle — Thu, 06 Jun 2013 17:30:54 GMT

That method works fine for me. Are you sure your field is the right type (long int)?

Re: Round to nearest 100th

ChrisBrannin — Sat, 11 Dec 2021 20:14:06 GMT

That method works fine for me. Are you sure your field is the right type (long int)?

I had no issue with it in arcmap attribute table field calculator. Just in IDLE... My code below:

import arcpy
import os, math
from arcpy import env


in_workspace = r"F:/Inventory_export_dev/testRnd"
rndValue = "int(round(!ELEVATION!, -2))"
fcList = []
fieldName = "SL_ELEV"


for dirpath, dirnames, filenames in arcpy.da.Walk(in_workspace, datatype="FeatureClass",type="All"):
    for filename in filenames:
        fcList.append(os.path.join(dirpath, filename))


for list in fcList:
    arcpy.AddField_management(list, fieldName, "SHORT", "", "", "", "", "NULLABLE")


print "Rounding ELEVATION field to SL_ELEV"


#Rounds values from [ELEVATION] to [SL_ELEV]
for elev in fcList:
    arcpy.CalculateField_management(elev, fieldName, rndValue, "PYTHON")

am I missing something?

Re: Round to nearest 100th

MathewCoyle — Thu, 06 Jun 2013 18:33:58 GMT

I would try printing out your elev value for each iteration of fcList to make sure it is what you expect.

Re: Round to nearest 100th

RhettZufelt — Sat, 11 Dec 2021 20:14:08 GMT

Looks like you are trying to round the ELEVATION variable before you have set it to anything.

Need to either set it or extract it from the attributes first.

Also, both your for loops are working the same data, in one you assign it to list, in the other you assign to elev. But, in both cases, you are still just itering through the values in fcList, so just as well do it in one swoop.

Think you are looking for something like this:

import arcpy
import os, math
from arcpy import env


in_workspace = r"F:/Inventory_export_dev/testRnd"
fcList = []



for dirpath, dirnames, filenames in arcpy.da.Walk(in_workspace, datatype="FeatureClass",type="All"):
    for filename in filenames:
        fcList.append(os.path.join(dirpath, filename))


for list in fcList:
    arcpy.AddField_management(list, fieldName, "SHORT", "", "", "", "", "NULLABLE")
    arcpy.CalculateField_management(list, "SL_ELEV", "int(round( !ELEVATION!, -2))", "PYTHON")

Haven't tested, but should go through each FC in your fcList add the field and populate it with the round value.

R_

Re: Round to nearest 100th

RhettZufelt — Thu, 06 Jun 2013 18:59:44 GMT

Deleted my last post after re-reading.

However, it looks like you can use one for loop to replace all three that you are running.

might try something like:

import arcpy import os, math from arcpy import env   in_workspace = r"F:/Inventory_export_dev/testRnd" fcList = []    for dirpath, dirnames, filenames in arcpy.da.Walk(in_workspace, datatype="FeatureClass",type="All"):     for filename in filenames:         arcpy.AddField_management(os.path.join(dirpath, filename), fieldName, "SHORT", "", "", "", "", "NULLABLE")         arcpy.CalculateField_management(os.path.join(dirpath, filename), "SL_ELEV", "int(round( !ELEVATION!, -2))", "PYTHON")

No need to put the filenames in a list if all you are going to do is iterate through them again. Just as well do the work on the first iteration.

Of course, this will errror out if any of the FC's in your in_workspace do not have the numeric ELEVATION field.

R_

Re: Round to nearest 100th

ChrisBrannin — Sat, 11 Dec 2021 20:14:11 GMT

Deleted my last post after re-reading.

However, it looks like you can use one for loop to replace all three that you are running.

might try something like:
import arcpy
import os, math
from arcpy import env


in_workspace = r"F:/Inventory_export_dev/testRnd"
fcList = []



for dirpath, dirnames, filenames in arcpy.da.Walk(in_workspace, datatype="FeatureClass",type="All"):
    for filename in filenames:
        arcpy.AddField_management(os.path.join(dirpath, filename), fieldName, "SHORT", "", "", "", "", "NULLABLE")
        arcpy.CalculateField_management(os.path.join(dirpath, filename), "SL_ELEV", "int(round( !ELEVATION!, -2))", "PYTHON")
No need to put the filenames in a list if all you are going to do is iterate through them again. Just as well do the work on the first iteration.

Of course, this will errror out if any of the FC's in your in_workspace do not have the numeric ELEVATION field.

R_

I see this works perfectly then. Is there an easy way to skip the files that do not have the elevation field?

Re: Round to nearest 100th

RhettZufelt — Sat, 11 Dec 2021 20:14:14 GMT

Replace the work part with this should do it:


for dirpath, dirnames, filenames in arcpy.da.Walk(in_workspace, datatype="FeatureClass",type="All"):
    for filename in filenames:
       if "ELEVATION" in [f.name for f in arcpy.ListFields(os.path.join(dirpath, filename))]:
         arcpy.AddField_management(os.path.join(dirpath, filename), "SL_ELEV", "SHORT", "", "", "", "", "NULLABLE")
         arcpy.CalculateField_management(os.path.join(dirpath, filename), "SL_ELEV", "int(round( !ELEVATION!, -2))", "PYTHON")
       else:
           print "no Elevation field for dataset ", filename

Of course, you can skip the else: part, only needed if you want it to do something when ELEVATION field not present.

R_

Re: Round to nearest 100th

ChrisBrannin — Sat, 11 Dec 2021 20:14:16 GMT

Replace the work part with this should do it:


for dirpath, dirnames, filenames in arcpy.da.Walk(in_workspace, datatype="FeatureClass",type="All"):
    for filename in filenames:
       if "ELEVATION" in [f.name for f in arcpy.ListFields(os.path.join(dirpath, filename))]:
         arcpy.AddField_management(os.path.join(dirpath, filename), "SL_ELEV", "SHORT", "", "", "", "", "NULLABLE")
         arcpy.CalculateField_management(os.path.join(dirpath, filename), "SL_ELEV", "int(round( !ELEVATION!, -2))", "PYTHON")
       else:
           print "no Elevation field for dataset ", filename

Of course, you can skip the else: part, only needed if you want it to do something when ELEVATION field not present.

R_

This is seriously great. I tried something like this with no luck. But now I understand why it did not work.

if "ELEVATION" == arcpy.ListFields(os.path.join(dirpath, filename)):

Thank you for your time with this.

Re: Round to nearest 100th

RhettZufelt — Sat, 11 Dec 2021 20:14:19 GMT

So you see that it was trying to compare a single string "ELEVATION" to a list of objects.

basically, could do something like:


fieldList = arcpy.ListFields(os.path.join(dirpath, filename))

for f in fieldList:
   if f.name == "ELEVATION":
         arcpy.AddField_management(os.path.join(dirpath, filename), "SL_ELEV", "SHORT", "", "", "", "", "NULLABLE")
         arcpy.CalculateField_management(os.path.join(dirpath, filename), "SL_ELEV", "int(round( !ELEVATION!, -2))", "PYTHON")

Which is the same thing, I just used list comprehension to shorten the list, iterator, and comparison into one line instead of three. (love list comprehension, just wish I were better at it...)

R_

Re: Round to nearest 100th

wilfredwaters — Wed, 28 Aug 2013 08:26:58 GMT

Is there a way to do this in raster calculator?

Would Int( Floor( [in_raster] + 0.5 ) ) suffice?

Or even Int( [in_raster] + 0.5 ) ?