Now, let's look at a dictionary client, another very useful and common application of symbol tables. So, in this case, we are going to write a client called Lookup CSV that [cough] is going to take three arguments. The first will be a file name, a so-called common separated value file and the next two arguments are integers which will tell us what to treat as keys and values in the file. In this example or CSV file relates URLs to IP addresses. So, each line has a URL and IP address and are separated by commas. And in general, a CSV file might have many fields separated by comma, comma. So, we number them zero, one, and so forth starting from the left. So, what we are going to do with this client is specify with integers which field is the key, and which is the value. So, if we call this client with second argument zero and third argument one, that means we want to use the URL field zero on the CSV file as the key, no one use the IP address that's field one in the CSV as the value, you want to associate keys with values. So the client will build a symbol table that makes us associations for every line in the file and this could be huge file. And then, if we want to look up the IP address associated with a given URL we can just type in URLs and the client will return the IP address, it'll do the look up. So, Adobe.com has got this IP address that's shown if this line here in the table, and so forth. Princeton.edu has this IP and ebay.edu is not in the file. Now, on the other hand, we could, from this same file, we could build a symbol table where we treat the IP address as the, as the key and the URL as the value. So, in that case, it'll build a symbol table with IP addresses as keys and we can type in an IP address and get the associated URL. So, with one client we can handle lookups of all kinds in CSV files. For example, here's another CSV file that from biology that deals with, amino acids and codons and names. So, in this case, the first field is three letters from the DNA sequence which, represents a codon. And certain codons have names, that's the amino acids. So, TCC is called serine, and so forth. And that's an association that's well known to biologist and then you can use this lookup CSV client to quickly get the name associated with any given codon. That's just another simple example. This is a very general tool. Any CSV file, you can pick any field as the key, any other field as the value. So here's still another example where we might use for a class list, which has the person's year of graduation, last name, first name precept name and login name. And so in the first call over here, we might use the login name as the key and the first name as the value. So, we type in somebody's login name we get their first name. And again, with the same client login is key and get the section as a value. So, all kinds of information processing that we might need to do for large amounts of data, represented in comma, comma separated value files this one client which is based on a symbol table will provide useful functionality. And here's the implementation there's very little to it given the symbol table API that we've articulated and the implementations that we have. So what do we do to get lookup CSV implemented? Well, first thing is to set up the input stream from the first argument, so that's our input file. And then, get the numbers of the fields, so the key and the value. And now build a simple table that associates strings with strings. Then there there's a while loop where we just read a new line in that read line, read line and then split according to comma into tokens in an array. And then, the index in the array is going to build the fields that we're going to use. So, the key is the string in the key field entry of the array, and the value is the string in the value field entry in the array, and we simpl y put that into symbol table. So, this value loop just builds the symbol table from the file. Then from standard input we take queries, just read a string, check if the symbol table contains the string. It, it doesn't, print not found. And if it does, print the value associated with the key. So, a very small amount of code based on a symbol table implementation that gives us the dictionary functionality.
