I imagine the film was completely different to the book - the book itself has a lot of politics in it (people find the first couple of hundred pages very hard to get into because there is so much politics, all to do with the story world, obviously), and the Sci-Fi elements take more of a back seat, in the grand scheme of things.

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Another one (with film adaptations, which are completely different to the book) is Richard Matheson's I Am Legend.