Callable library question: How to truncate a polymake::Vector?

[mws]

I am using the callable library of Polymake 2.14.

Let's say I define a vector of size 4 in my C++ program, i.e.,

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polymake::Vector<Rational> vec {4};

After doing some computations I need to discard the last element. If vec would be of type std::vector, I'd just use .pop_back(), but this doesn't seem to work. What's the "right" way to do it?

[paffenholz]

You can use the "slice" method for this. There are two variants

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vector.slice(<Set>); vector.slice(a,b);

The first requires a (Generic)Set giving a valid set of indices of the vector, the second cuts out a continuous part of length b of the vector, starting at index a. Also here, a+b-1 must still be a valid index. If you put b=0, then you get the slice from a to the end of the vector. In this case you can also omit b (0 is the default for b).

Andreas

[gawrilow]

Suggestions made by Andreas would produce a new object, the initial vector would not change. I guess, the original question was more aiming at a mutating method. For that, the answer is resize().

[mws]

Yes, I am interested in changing the existing vector. So

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vec.resize(n)

keeps the first n elements and discards the rest?

[gawrilow]

Exactly.