Symbol size proportional to frequency

Question

I would like to plot on QGIS these coordinates using a different color for the individuals and a different size of the symbol when the same individual is detected in the same zone (same coordinates). I can give different colors to the individuals using the command: double click on the layer-->style-->"categorized". But I can't find out how to give different size to the symbols.

For example, the individual Gen26 is detected in the same position 4 times (Ua8546, Ua8547, Ua8552, Ua8559), and in another position twice (Ua8542, Ua8543). I would like to give bigger dimensions to the symbol when is detected 4 times than when is detected twice; of course, maintaining the same color for each individual.

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@she_weeds and @kazuhito, I've found a problem: the method seemed to work but saw one thing. The points are different in colors depending on individuals, also the points seem to have different sizes depending on frequency of occurrence BUT one individual detected only once in a point has the same size (big) of another individual detected different times in the same point. I've simplified (and modified) the dataset I posted one week ago

Gen20 has the same dimensions of Gen16, but Gen16 is detected 5 times in that position, whereas Gen20 once. I used this function: count_distinct("ID", group_by:=geom_to_wkt($geometry)). I'm sorry, I thought it worked but I can't understand how to solve this problem (I tried in these days to solve, but nothing). Hoping in your another magic answer

Answer 1

Using Kazuhito's suggestion you could use a data-defined override in the symbology without changing your data.

When selecting the Categorised style type edit the "underlying" symbology by clicking 'Change...' (see blue circle below)

Select the data-defined override for "Size" and paste this expression in the expression string builder:

count_distinct("UID", group_by:=geom_to_wkt($geometry))

Then select your Column and click Classify.

Here is the resulting output of the data you presented, with the numeric value of the above count shown above each circle.

You can then add a multiplier to that expression or a min/max/clamp expression to modify the scale accordingly.

Answer 2

EDIT: I've overseen that you want to keep your original table! Here is the right query:

1. Create a Virtual Layer like:

   WITH count_subquery AS (
       SELECT count(id) AS count, individual FROM your_table 
           GROUP BY individual)
       SELECT a.*, b.count FROM your_table a, count_subquery b
           WHERE a.individual=b.individual
   

2. For the new Virtual Layer set the data defined Symbol Size in the Properties (choose Edit) from the field count from Fields and Values in the Expression string builder.

Answer 3

Another approach using the Field Calculator.

(1) Create a new field (dupl in the above example) using an expression:

count_distinct( "ID", group_by:=geom_to_wkt($geometry), filter:="Individual"='Gen26')

This counts duplicated points which has the name Gen26. Output looks like below image.

(2) Set color, and size of points according to this field. My suggestion is to use categorized.

Classify the symbol according to the individual field, and size is set as data-defined override (large epsilon).