No isimag() curioso

[Daniel J Sebald]

In working with the fftfilt() routine and wanting to know if the inputs 
were purely imaginary I wondered why there is no such thing as isimag(). 
 It seems as though it would be as useful as or more useful than 
iscomplex().

Here's the thing: iscomplex() appears to be simply the complement of 
isreal(), unless I'm missing a more sophisticated use of syntax:

octave:5> x = 1
x =  1
octave:6> [isreal(x) iscomplex(x)]
ans =

   1   0

octave:7> x = i
x =  0 + 1i
octave:8> [isreal(x) iscomplex(x)]
ans =

   0   1

octave:9> x = 1+i
x =  1 + 1i
octave:10> [isreal(x) iscomplex(x)]
ans =

   0   1

octave:11>

I ask, What's the point of having a function that is simply !isreal()? 
On the other hand isimag(), which is equivalent to "all (real (x) == 0)) 
&& !isreal (x)", would be a nice shorthand.

Just an observation.  Usually duplication of function (or its 
complement) is weeded out of programming languages.

Dan