Short way to eliminate a list from a matrix, if the first element is negative [closed]

I'm looking for a short way to eliminate a list from a matrix, if the first element of the list is negative. I've come up with this:

a = {{5, -1, 3, -2}, {-4, -3, -3, -4}, {2, -1, 5, 5}}

f[x_] := Table[x, 4];
Pick[a, f /@ UnitStep[a[[All, 1]]], 1] /. {} -> Nothing


The output is and should be:

{{5, -1, 3, -2}, {2, -1, 5, 5}}


In my example, all lists have a length of 4, this explains the Table[x, 4]. A general case would be more interesting.

closed as off-topic by mikado, xslittlegrass, MarcoB, happy fish, m_goldbergApr 17 '17 at 15:38

This question appears to be off-topic. The users who voted to close gave this specific reason:

• "This question arises due to a simple mistake such as a trivial syntax error, incorrect capitalization, spelling mistake, or other typographical error and is unlikely to help any future visitors, or else it is easily found in the documentation." – mikado, xslittlegrass, MarcoB, happy fish, m_goldberg
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• Select[a,#[[1]] >= 0&] – user46676 Apr 16 '17 at 19:11

Pick[a,#>=0&@@@a]

{{5, -1, 3, -2}, {2, -1, 5, 5}}