if we have $p$ variables, the number of scatter plots we have is :
$p(p-1)/2$.
Why is this so? Is there any one who can explain this formula?
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$\begingroup$ Does this entry in Wikipedia help? $\endgroup$– mdeweyAug 12, 2016 at 11:50
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2 Answers
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When you have p variables and would like to have scatter plots for 2 variables each then number of combinations come upto p combination 2(Pc2 # P subscript C subscript 2) by expanding the formula you get p(p-1)/2
sorry i don't know to add subscripts here so i wrote subscript
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When you represent all the scatter plots, you only want to plot the pairs of different variables. And:
$$\binom{p}{2}=\frac{p(p-1)}2$$
As @NickCox stressed, the plot of $y$ versus $x$ contains the same points as that of $x$ versus $y$ (up to exchange of axes).
answered Aug 12, 2016 at 10:11