CODEWITHSUNDEEP
expressionmapboxmapbox-gl-jsmapbox-gl
Lauren
Lauren

Reputation: 1085

Mapbox expression for calculating mean of existing properties only

I have a large map layer in which each feature has separate properties for each week of the year. On a button click, I want to style each feature with the mean of the selected properties.

Here is a reproducible example: https://codepen.io/leol222/pen/JjNKEpZ

In this example, I have 'selected' to calculate the mean of properties week1, week2, and week3 on button click. I can roughly achieve what I want with a Mapbox expression that creates the variable mean by summing each week property value with get and dividing by the number of weeks I have selected:

  const colors = [0, '#FCCE25', 2, '#EC7754', 5, '#9B179F', 12, '#0D0887'];
  const selectedWeeks = ['week1', 'week2', 'week3'];
  const expression = selectedWeeks.map(wk => ['get', wk]);
  // ['get', 'week1'], ['get', 'week2'], ['get', 'week3']
  
  document.getElementById('btn').addEventListener('click', () => {
    map.setPaintProperty('shapes', 'fill-color', 
     ['let', 'mean', ['/', ['+', ...expression], expression.length],
     ['interpolate', ['linear'], ['var', 'mean'], ...colors]
     ]
    )
  });

The problem I have with this expression is that some features do not include all of the selected week properties. In these features, the ['get', <selected week>] expression returns null, which then calculates the mean as null, as shown by the black styled squares below:

enter image description here

The black squares are features that do not include all 3 selected weeks of data. What I want my expression to do is to calculate the mean for all of the features by omitting any missing properties. So in this case, features 2 would simply omit the missing week1 property and instead calculate the mean of week2 and week3, resulting in a new mean var of 10.5.

Upvotes: 0

Views: 521

Answers (1)

Edith
Edith

Reputation: 181

Only hit on the way :

It should be adapted, but instead of using ['get', propertyName] you could generate it with an expression such as

const getPropertyValue = propertyName => [
  'case',
  ['boolean', ['has', propertyName], true], 
  ['get', propertyName],
  0
];

which here use the property value if it exist or 0 otherwise. -> should be changed for the mean, not sure how yet.

Upvotes: 0

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