I want to get the data in a circle from a large square plot.

If the data includes only two columns or more columns which is number style,
I can do it.
But if the data includes other columns which is not number style (e.g.
species name), I donot know how to do it. And I donot want to delete the
columns because it is useful to me.
e.g.          species    x      y
                    a         12    20
                    b         20    50
                    c         14    25
                    ...        ...    ...

Thanks!

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