How to get rid of duplicate values in d3.js?

@denis 

To get rid of duplicate values in d3.js, you can use the d3.nest() and d3.map() functions to group and filter the data. Here's an example:

1. Load the d3 library in your HTML file:

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<script src="https://d3js.org/d3.v6.min.js"></script>

1. Create a function to remove duplicates from an array:

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function removeDuplicates(data) {
    return Array.from(new Set(data));
}

1. Use the d3.nest() function to group the data by a unique key:

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var nestedData = d3.nest()
    .key(function(d) { return d.key; })
    .entries(data);

1. Use the d3.map() function to remove duplicates from the nested data:

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var uniqueData = d3.map(nestedData, function(d) { return d.key; }).values();

1. You can then use the uniqueData array in your d3.js visualization without any duplicate values.

This is a simple example of how to remove duplicates in d3.js. Depending on the structure of your data, you may need to modify this code to suit your specific requirements.