ArcMap – Update Field Column Data from Another Column using Python Parser in Field Calculator

Esri’s ArcMap 10.4 lets you to use Field Calculator to update the values in one field based on another. The process requires that you firstly have the data merged from another layer file. This involves using the join and relate function which you can select from the menu option by right clicking on the layer. Once you have merged the data you can then update one column’s data from another within the main attribute table that is opened. Please see How to Merge Data from a Points Layer to a Polygons Layer by spatial location.

ArcMap Field Calculator Dialogue

Using Python parser in Field Calculator to update data in columns

  • Step 1 – Open the attributes table from the layer you have merged the data to:
    Highlight or select the rows you want to update then left click on the column header that you want to replace/update the data to. Selecting the rows will only update the data which you have selected.




  • Step 2 – Select start editing from the top menu:
    A Start Editing dialogue box will appear. Select the layer or workspace you will being to edit. This should be the layer that contains the data that is already merged. Click OK








  • Step 3 – Using field calculator select the data type and python script option boxes:
    Select python parser and the data type option for the values you are going to update. Below the option that says Code Block you will see the header of the field you will update. Add the header of the column which contains the data you want to replace. Eg. “!MsgComment!”
ArcMap Field Calculator
ArcMap 10.4 Field Calculator
ArcMap Editing Dialogue Box
Edit Layer Dialogue Box
ArcMap Field Calculator Dialogue
Field Calculator Dialogue

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