Unitize[x] gives when x is zero, and when x has any other numerical value.
Convert numerical values to zero or one:
Replace values in a matrix with zeros or ones:
Show a plot that emphasizes structure:
UnitStep KroneckerDelta Boole Sign DiracDelta Clip
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when x is zero, and 
when x has any other numerical value.
when x is zero, and when x has any other numerical value.