GrouBy Data Expression

[JanelleShank]

Good Afternoon, All!

I have a dataset of voting results and I can trying to create a data expression that returns the MAX value of registered voters within each district and then add the total of each MAX value to find the total number of those registered. I have written a data expression using the GoupBy function, however, it is returning a null value. I have provided examples of my data expression and data below. 

var fs = FeaturesetByPortalItem(Portal("https://bedfordplanning.maps.arcgis.com"), "78eb292ce436450b85dc249bd3069741", 0, ["Precinct_name", "Reg_voters"], false)

var out_dict = {

  fields: [

    {name: "Precinct_Name", type: "esriFieldTypeString"},

    {name: "Reg_voters", type: "esriFieldTypeString"}

  ],

  features: [],

  geometryType: ""

}

var maxvotes = GroupBy("out_dict", 'Precinct_Name', {name: 'Reg_voters', expression: 'Reg_Voters', statistic: "MAX"})

Thank you,

Janelle

[KenBuja]

You're using out_dict in the GroupBy, but you haven't assigned any records to it. Why aren't you using fs in the GroupBy?

[JanelleShank]

I thought by using "out_dict", I was assigning a new variable.

[KenBuja]

The first parameter of the GroupBy function is the FeatureSet that contains the data, which should be fs. The out_dict variable is just an empty FeatureSet you've created.

[JanelleShank]

Thank you, I'll give that try. 

[JanelleShank]

When I replaced "out_dict" with fs, I got an error that it could not execute the expression. Do you happen to have any idea of where I am going wrong?

[KenBuja]

When using variables, don't encase them in quotes.

var maxvotes = GroupBy(fs, 'Precinct_Name', {name: 'Reg_voters', expression: 'Reg_Voters', statistic: "MAX"})

[JanelleShank]

Thank you. I removed the quotes from the variable and the expression was able to run this time. However it returned a "null" value when it should return a table, like the one below. 

Do I need to return to the empty FeatureSet?

[KenBuja · Accepted solution]

Since your data is private, I can't test it. However, I was able to test using a public service and it worked as expected, returning two items in the table with the maximum value for each aggregationMethod

var fs =  FeatureSetByPortalItem(
    Portal("https://www.arcgis.com"),
    // portal item id
    "7b1fb95ab77f40bf8aa09c8b59045449",
    0, // layer id
    ["*"], // fields to include
    false // include or exclude geometry
  );

GroupBy(fs, 'aggregationMethod', {name: 'TOTPOP_CY', expression: 'TOTPOP_CY', statistic: "MAX"})

[JanelleShank]

Thank you for your help on this! Your code helped me refine my expression and I also noticed that I had my Item number incorrect in my expression and once that was fixed I was able to apply the correct expression. 

Thank you, again!

Best,

Janelle