Table-1 Data

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Class fun survey: do it now

As another example of how data is stored and manipulated in the computer, we'll look at "table data" -- a common a way to organize strings, numbers, dates in rectangular table structure. In particular, we'll start with data from the social security administration baby name site.

Social Security Baby Name Example

table organized as fields and rows

Tables Are Very Common

Much of the information stored on computers uses this table structure. One "thing" we want to store -- a baby name, someone's contact info, a craigslist advertisement -- is one row. The number of fields that make up a row is fairly small -- essentially the fixed categories of information we think up for that sort of thing. For example one craigslist advertisement (stored in one row) has a few fields: a short description, a long description, a price, a seller, ... plus a few more fields.

The number of fields is small, but the number of rows can be quite large -- thousands or millions. When someone talks about a "database" on the computer, that builds on this basic idea of a table. Also storing data in a spreadsheet typically uses exactly this table structure.

Table Code

We'll start with some CS101 code -- SimpleTable -- which will serve as a foundation for you to write table code. Run the code to see what it does.


table-1-1

Table Query Logic


table-1-2

The above code loops over all the rows, and the if-statement prints just the rows where the test is true -- here testing if the rank field is equal to 6, but really the if-statement could test anything about the row.


table-1-3

The row object has a row.getField("field-name") function which returns the data for one field out of the row. Each field has a name -- one of "name" "rank" "gender" "year" in this case -- and the string name of the field is passed in to getField() to indicate which field we want, e.g. row.getField("rank") to retrieve the rank out of that row.

You can test if two values are equal in JavaScript with two equal signs joined like this: ==. Using ==, the code to test if the name field is "Alice" is row.getField("name") == "Alice"

Note that a single equal sign = does variable assignment and not comparison. It's a common mistake to type in one equal sign for a test, when you mean two equal signs. For this class, the Run button will detect an accidental use of a single = in an if-test and give an error message. The regular less-than/greater-than type tests: < > <= >= work as have seen before.

Table Query Examples


table-1-4

Write in code above to solve these problems:

Solution code:

If logic inside the loop:

table = new SimpleTable("baby-2010.csv");
for (row: table) {
  if (row.getField("name") == "Alice") {
    print(row);
  }
}
// Change string to "Robert", "Bob", etc.

  if (row.getField("rank") == 1) {
    print(row);
  }

  if (row.getField("rank") < 10) {
    print(row);
  }

  if (row.getField("rank") <= 10) {
    print(row);
  }

  if (row.getField("rank") > 990) {
    print(row);
  }

  if (row.getField("gender") == "girl") {
    print(row);
  }

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