Editing Fields Back to <Null>

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10-24-2013 08:01 AM
ChristinaDeFrancesco
New Contributor
Hi all,

I have a set of data with some fields in the Attributes Table that default to <Null>.  If I edit a particular field, then try to set it back to a no data cell, the cell value is no longer <Null> but simply blank.  How do I change my field cell back to <Null> so I can run a query (for Null values) on it?  I am using ArcGIS for Desktop 10.1 SP1. 

Thanks!
Christina
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9 Replies
TimWitt
Frequent Contributor
Christina,

Can't you just select the records you want to be null, the right click the column and use the field Calculator and Calculate them using "null" (without the quotes) ?

Tim
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ChristinaDeFrancesco
New Contributor
Hi Tim,

I'm not sure how to select specific cells vs an entire row or column.  In playing around with your idea, my edit session will only allow me to select an entire column.  Also, when I tried the Field Calculator ([Field]="Null") it left my <Null> cells the way they were, and any cell that contained information was assigned a number (0) so still not the <Null> value I'm looking for. 

I have tried simply changing the cell to a text "<Null>" but the query I'm running (currently on Symbology to display a value based on a <Null> option but I would also like to display data based on a definition query- [Field] IS NOT NULL) but it seems the text "Null" is not read by ArcGIS the same way as the coded <Null>. 

I hope this all makes sense!
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TimWitt
Frequent Contributor
Christina,

you need to write null without the quotations in the expression box (i.e. [Field]=null)  . This will set your fields to <Null>.
Also even though it selects your entire row, it will only calculate the Attribute Field, where your right clicked its heading and chose Field Calculator.

Tim
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ChristinaDeFrancesco
New Contributor
Hi Tim,

I see what you're saying- that works beautifully.  I'm wondering, however, if there is a way to do this same technique on only single cells at a time? I have 400+ data points, from which I only want a select few cells in a field column to change to Null; if I changed an entire column I would have to go back and re-enter data in cells that need data.  Any thoughts on a more cell-specific technique?
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TimWitt
Frequent Contributor
In your attribute table you can select the row you would like to change a cell in. Ctrl +left click the grey square all the way to your left, of your desired row. Repeat that for each row you would like to change a cell in. Once you have selected all the rows you would like to change to <null>, perform the field calculation outlined above. This will only calculate the cells of your collected row.
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ChristinaDeFrancesco
New Contributor
Tim,

This is perfect!  Thank you!
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TimWitt
Frequent Contributor
No problem! Don't forget to mark the post that answered your question by clicking the greyed out question mark to the right of it!
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ChristinaDeFrancesco
New Contributor
Oops, I'm not sure I can do that since when I originally created this thread I designated the Discussion type rather than Question.
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TimWitt
Frequent Contributor
Don't worry about it, upvoting the helpful posts will also show a person with the same problem how to solve this problem. :)
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