Question: filter for Map used in a Matrix (involving `if`)

Hi, Sorry if a question like this has already been answered, but I didn't find any similar ones. I have a matrix that may look like this: M:=Matrix([[1,[0,0,0],[0,0,0]],[lambda,[0,0,0],[1,1,0]],[lambda,[1,1,0],[0,0,0]],[lambda^2 ,[1,1,0],[1,1,0]]]); only much larger... maybe with RowDimension 200000. Is it possible to use LinearAlgebra:-Map involving some conditioning on different rows. Say "Map the first element of each row to zero if the second and third elements are equal". I can do operation in different columns like: Map[(i,j)->evalb(j=3)](x->2*x,M) for example. But I do not know how to compare different columns or involve more than one. Will a "do" loop have the same efficiency as Map or map? Thank you all for reading and any comments are welcome, Cheers, Al.
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