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This question already has an answer here:

I have the following array of numbers:

a = {{0, 2, 5}, {3, 5, 1}, {4, 0, 5}, {8, 3, 4}, {0, 8, 6}}; 

then I make a list of the first row with

r = a[[All, 1]]

I would like to take just the elements where the first number is equal to 0. I have tried with

TakeWhile[a, r = 0]

but I didn't get a result.

Any suggestions?

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marked as duplicate by Kuba, m_goldberg, bbgodfrey, Sjoerd C. de Vries, Dr. belisarius Mar 5 '15 at 15:20

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    $\begingroup$ a[[All, 1]] isn't the first row, it's the first column $\endgroup$ – Sjoerd C. de Vries Mar 5 '15 at 14:54
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You might try

Cases[a,{0,__}]
(* {{0, 2, 5}, {0, 8, 6}} *) 
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  • $\begingroup$ @GregorioMartinez: You're most welcome. Please also accept my answer, if it fits your needs. $\endgroup$ – Jinxed Mar 5 '15 at 18:18

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