In the bar chart shown below, the well identifier is shown on the x axis, and production is shown on the y axis.  There are a lot of wells in this data set, but you only want to show the top x, let's say top 10.  You want the visualization to be dynamic and always update.  This can be done is several ways, one way is to apply a custom expression to the x axis.  


Applying the expression shown below to the x axis results in only 10 wells being shown, and all other results being lumped into a bar called "All Other Wells".  The DenseRank function is used, because if there is a tie (i.e. two wells produce the same amount), they will be counted as one well.  You could also use the Rank function.  See here for an explanation of Rank versus Dense Rank.    

If(DenseRank(Sum([Production]) over ([c.UWI]),"desc")<=10,[c.UWI],"All Other Wells") as [UWI]

When writing the expression, just make sure that the continuous column (in this case, Production) is the same in the expression as on the y axis.  Also note that the "as [UWI]" part of the expression is simply renaming the label.