Using SCRIPT_REAL in Data Source Tab in Tableau

Question

I want to create a calculated field in my data source table (in Data Source tab of my workbook). However, Tableau is complaining that the field contains an aggregate calculation data and so it depends on the visualization's level of detail. Here is my script (using TabPy):

SCRIPT_REAL("import numpy as np 
return (2*np.array(_arg1)).tolist()",
SUM([Wind Speed]))

In this case, all the rows in this calculated field are shown as null.

However, when I replace the SCRIPT_REAL with the following, it works:

2*SUM([Wind Speed])

Yet, in both cases, I'm using SUM [an aggregate function], so why does it work in this case but not when I'm using SCRIPT_REAL?

All I want to do is use SCRIPT_REAL to calculate values for a new field (row-wise) and add it to my data table. What am I missing?

Script_Real is a table calculation. Read the manual about table calcs, especially partitioning and addressing — Alex Blakemore, Apr 12 '17 at 23:24
@AlexBlakemore thanks -- so, can this be made to work in the Data Source tab if I correctly use partitioning and addressing? — , Apr 13 '17 at 13:18
Should be able to. Table calcs can be a bit tricky, there are more knobs to turn than just getting the formula correct. Most important of those are understanding how partitioning and addressing work. Get comfortable with those concepts and you should be ok. — Alex Blakemore, Apr 14 '17 at 15:53

e h · Accepted Answer · 2017-04-14T16:29:25.067

Without knowing what your data looks like it is hard to say what is going on. The calculation is valid:

One thing that can help a lot when debugging these kinds of problems is to print the data before returning it so that you can inspect it in the console.

SCRIPT_REAL(
"import numpy as np
values = (2*np.array(_arg1)).tolist()
print values
return values"
,
SUM([Value])
)

You can then look at TabPy and see:

INFO:__main__:{"INFO": "Initializing TabPy..."}
INFO:__main__:{"INFO": "Done initializing TabPy."}
INFO:__main__:{"INFO": "Web service listening on port 9004"}
INFO:__main__:{"INFO": "function to evaluate=def _user_script(tabpy, _arg1):\n import numpy as np\n values = (2*np.array(_arg1)).tolist()\n print values\n return values\n"}
[14, 20, 32, 44, 58, 52, 40, 66]
INFO:tornado.access:200 POST /evaluate (172.17.0.1) 53.75ms

So that calculation computes the values: [14, 20, 32, 44, 58, 52, 40, 66]

As Alex Blakemore mentioned, these calculations are "Table Calculations" and will be computed on "Table" by default. That means that Tableau will pass all the values in the view at once to TabPy. Basically, it passes an array and you get an array back (like in the example above). If you change the "compute by" setting it can pass fractions of the data, or even each row individually, but generally "Table" is best since it passes all the data at once to TabPy and then TabPy passes all the results back in an array.

=========================================

Update: a "table calculation" is run on the data in the "view" it cannot be pre-computed in the underlying data since there is no way of knowing what you will be visualizing. If you take a look in the data preparation pane you will see a message about this:

Basically, a "table calculation" is run on demand and is ephemeral. If you want the values persisted then I recommend running a standard calculation, or pre-computing the values in the data source. TabPy depends on these ephemeral type of calculations so it is good for exploring data, but not for persisting it.

Thanks. As you demonstrated, the script works fine when applied to a visualization/chart view. My issue is when you try to enter that same exact script into the underlying data table on the Source Data tab (as a calculated field), Tableau tells me that the formula uses aggregate data and hence depends on the visualization. Note: this is not an error, it just refuses to run the script until I use that calculated field in an actual view (like the chart you just put together). I.e., it seems to require that the script be part of a "shelf" (to use Tableau-speak). — , Apr 14 '17 at 16:12
I hope my comment clarifies the issue. It's working fine when I move the calculation to a shelf (on some visualization), it wont work when try to augment my underlying data table (in Data Sources tab) with a calculated fields based on this exact same script. — , Apr 14 '17 at 16:14

Using SCRIPT_REAL in Data Source Tab in Tableau

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