I am trying to manage a matrix in Mathematica that has the general architecture
{{a1,b1},{a2,b2}...}
I would like to combine all of the lists that have the same the first value and transform it to a new list of lists of the second values,
For example,
If I have the list
{{1,2},{1,5},{1,30},{2,6},{3,8},{3,30},{4,1}}
I would like the output to be
{{2,5,30},{6},{8,30},{1}}
I would then like to remove any of the list elements that contain only 1 value
So that my final output would be
{{2,5,30},{8,30}}
I am still new to data manipulation in mathematica and really do not know where to begin on this problem