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simpler neural network language models
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uh so multi perceptrons and so on it
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really introduces the language modeling
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framework and then uh here in this video
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we're going to focus on the Transformer
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neural network itself okay so I created
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a new Google collab uh jup notebook here
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and this will allow me to later easily
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share this code that we're going to
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develop together uh with you so you can
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follow along so this will be in a video
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description uh later now here I've just
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done some preliminaries I downloaded the
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data set the tiny Shakespeare data set
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at this URL and you can see that it's
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about a 1 Megabyte file then here I open
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the input.txt file and just read in all
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the text of the string and we see that
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we are working with 1 million characters
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roughly and the first 1,000 characters
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if we just print them out are basically
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what you would expect this is the first
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1,000 characters of the tiny Shakespeare
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data set roughly up to here so so far so
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good next we're going to take this text
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and the text is a sequence of characters
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in Python so when I call the set
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Constructor on it I'm just going to get
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the set of all the characters that occur
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in this text and then I call list on
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that to create a list of those
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characters instead of just a set so that
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I have an ordering an arbitrary ordering
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and then I sort that so basically we get
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just all the characters that occur in
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the entire data set and they're sorted
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now the number of them is going to be
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our vocabulary size these are the
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possible elements of our sequences and
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we see that when I print here the
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characters there's 65 of them in total
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there's a space character and then all
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kinds of special characters and then U
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capitals and lowercase letters so that's
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our vocabulary and that's the sort of
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like possible uh characters that the
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model can see or emit okay so next we
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will would like to develop some strategy
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to tokenize the input text now when
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people say tokenize they mean convert
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the raw text as a string to some
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sequence of integers According to some
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uh notebook According to some vocabulary
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of possible elements so as an example
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here we are going to be building a
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character level language model so we're
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simply going to be translating
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individual characters into integers so
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let me show you uh a chunk of code that
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sort of does that for us so we're
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building both the encoder and the
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decoder
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and let me just talk through what's
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happening
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here when we encode an arbitrary text
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like hi there we're going to receive a
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list of integers that represents that
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string so for example 46 47 Etc and then
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we also have the reverse mapping so we
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can take this list and decode it to get
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back the exact same string so it's
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really just like a translation to
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integers and back for arbitrary string
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and for us it is done on a character
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level
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now the way this was achieved is we just
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iterate over all the characters here and
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create a lookup table from the character
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to the integer and vice versa and then
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to encode some string we simply
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translate all the characters
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individually and to decode it back we
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use the reverse mapping and concatenate
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all of it now this is only one of many
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possible encodings or many possible sort
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of tokenizers and it's a very simple one
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but there's many other schemas that
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people have come up with in practice so
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for example Google uses a sentence
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piece uh so sentence piece will also
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encode text into um integers but in a
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different schema and using a different
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vocabulary and sentence piece is a
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subword uh sort of tokenizer and what
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that means is that um you're not
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encoding entire words but you're not
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also encoding individual characters it's
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it's a subword unit level and that's
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usually what's adopted in practice for
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example also openai has this Library
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