If you pass in a node-set of authors, as shown here, it should work:. But if you pass in a string containing the XPath expression, it definitely won't work. Each of these xsl:call-template calls produce an error when executed:. If you need to parameterize aspects of an XPath expression, you can typically get by with parameterized predicate expressions, as shown here:.
This means you can't parameterize the select expression and pass in a string value. In fact, there really isn't a good way to accomplish this without either running a two-pass transformation or modifying the XSLT document programmatically before executing the transformation.
First, you run a transformation to generate the XSLT document with the "right" sort key embedded. For example, when the user clicks on a table column for sorting purposes, just use XPath to programmatically identify the select attribute in the XSLT document and modify its value before executing the transformation again. The sortable page is shown in Figure 5. The complete source code for this example is available for download with this article at the link at the top of this article.
The problem is that I want to generate a table header that includes the name of each element but remains generic. Any ideas? If you are, use an xsl:for-each statement to walk through each of its child elements to output its name, as shown here:. You can also accomplish this using xsl:apply-templates instead of xsl:for-each , but it requires the use of XSLT modes.
The XSLT language offers template modes to help deal with situations in which a given set of nodes needs to be processed in multiple passes. For example, your original program could be rewritten as shown in Figure 7. Modes play an important role in XSLT's declarative programming model and are often required when you have to deal with complex transformations.
Here's the sample equation that I'm using:. A The reason this turns out to be quite difficult is that XSLT variables don't behave like variables in most imperative programming languages. Nevertheless, you'll need to use them to solve this problem along with the help of recursion. Marvin Smit, an attendee at a recent conference at which I appeared, offered an elegant solution that uses a combination of xsl:apply-templates and xsl:value- of instructions to recursively process the equation see Figure 8.
I've provided the equation document, this solution, and a procedural solution which uses named templates and xsl:call-template in the sample code associated with this column. There is an overload that takes an IXPathNavigable reference. How do I get the result of a transform that returns text without writing it to a file? I need it as a string. In sketches that involve parsing data from a file or the web, you might get hold of that data in the form of an array of strings or as one long string.
This is where these two new functions, split and join , will come in handy. It takes two arguments, the String object to be split and the delimiter. The delimiter can be a single character or a string. Here is an example using a comma as the delimiter this time passing in a single character: ','.
If you want to use more than one delimiter to split up a text, you must use the Processing function splitTokens. Numbers in a string are not numbers and cannot be used in mathematical operations unless you convert them first. The reverse of split is join. The join function also takes two arguments, the array to be joined and a separator.
The separator can either be a single character or a string of characters. The join function, however, allows you to bypass this process, achieving the same result in only one line of code. Data can come from many different places: websites, news feeds, spreadsheets, databases, and so on. Let's say you've decided to make a map of the world's flowers. If you are really lucky, you might find a Processing library that hands data to you directly with code.
Maybe the answer is to just download this library and write some code like:. In this case, someone else has done all the work for you. They've gathered data about flowers and built a Processing library with a set of functions that hands you the data in an easy-to-understand format. This library, sadly, does not exist not yet , but there are some that do. For example, YahooWeather is a library by Marcel Schwittlick that grabs weather data from Yahoo for you, allowing you to write code like weather.
There is still plenty of work to do in the case of using a library. Let's take another scenario. If the data is online and your web browser can show it, shouldn't you be able to get the data in Processing?
Passing data from one application like a web application to another say, your Processing sketch is something that comes up again and again in software engineering.
Unfortunately, mlb. While possible, this solution is much less desirable given the considerable time required to read through the HTML source as well as program algorithms for parsing it. Each means of getting data comes with its own set of challenges. The ease of using a Processing library is dependent on the existence of clear documentation and examples. One other note worth a mention about working with data.
You don't want to be debugging your data retrieval process at the same time as solving problems related to algorithms for drawing. In keeping with my one-step-at-a-time mantra, once the meat of the program is completed with dummy data, you can then focus solely on how to retrieve the actual data from the real source.
Let's begin by working with the simplest means of data retrieval: reading from a text file. Text files can be used as a very simple database you could store settings for a program, a list of high scores, numbers for a graph, etc.
In order to create a text file, you can use any simple text editor. The individual lines of text in the file each become an individual element in the array. Text from a file can be used to generate a simple visualization.
Take the following data file. Looking at how to parse a csv file with split was a nice learning exercise. In truth, dealing with csv files which can easily be generated from spreadsheet software such as Google docs is such a common activity that Processing has an entire built-in class called Table to handle the parsing for you.
Processing's loadTable function takes comma-separated csv or tab-separated tsv values and automatically places the contents into a Table object storing the data in columns and rows. This is a great deal more convenient than struggling to manually parse large data files with split.
It works as follows. Let's say you have a data file that looks like:. Now I've missed an important detail. Take a look again at the data. Notice how the first line of text is not the data itself, but rather a header row. This row includes labels that describe the data included in each subsequent row.
The good news is that Processing can automatically interpret and store the headers for you, if you pass in the option "header" when loading the table. In addition to "header" , there are other options you can specify. For example, if your file is called data. If it also has a header row, then you can specifiy both options like so: "header,csv". A full list of options can be found on the loadTable documentation page.
Now that the table is loaded, I can show how you grab individual pieces of data or iterate over the entire table. Let's look at the data visualized as a grid. In the above grid you can see that the data is organized in terms of rows and columns. One way to access the data, therefore, would be to request a value by its numeric row and column location with zero being the first row or first column.
This is similar to accessing a pixel color at a given x,y location, though in this case the y position row comes first. The following code requests a piece of data at a given row, column location. For example, I could pull out a specific row from the Table. Note in the above line of code that a Table object refers to the entire table of data while a TableRow object handles an individual row of data within the Table.
Once I have the TableRow object, I can ask for data from some or all of the columns. The method getRow returns a single row from the table. If you want to grab all the rows and iterate over them you can do so in a loop with a counter accessing each row one at a time.
The total number of available rows can be retrieved with getRowCount. If you want to search for a select number of rows within the table, you can do so with findRows and matchRows. In addition to being read, Table objects can be altered or created on the fly while a sketch is running. Cell values can be adjusted, rows can be removed, and new rows can be added. For example, to set new values in a cell there are functions setInt , setFloat , and setString. To add a new row to a Table , simply call the method addRow and set the values of each column.
To delete a row, simply call the method removeRow and pass in the numeric index of the row you would like removed. For example, the following code removes the first row whenever the size of the table is greater than ten rows. The following example puts all of the above code together. Notice how each row of the table contains the data for a Bubble object. Here, the distance between a given point and a circle's center is compared to that circle's radius as depicted:.
In the code below, the function returns a boolean value true or false depending on whether the point mx,my is inside the circle. Notice how radius is equal to half the diameter. What if your data is not in a standard format like a table, how do you deal with it then?
One of the nice features about loadStrings is that in addition to pulling text from a file, you can also grab a URL. For example:. Converting the array into one long string can make things a bit simpler. As you saw earlier in the chapter, this can be achieved using join.
You can take advantage of the text manipulation functions you learned — indexOf , substring , and length — to find pieces of data within a large block of text. Take, for example, the following String object:. My algorithm would be as follows:. I can add some error checking and generalize the code into a function:. With this technique, you are ready to connect to a website from within Processing and grab data to use in your sketches. For example, you could read the HTML source from nytimes.
However, HTML is an ugly, scary place with inconsistently formatted pages that are difficult to reverse engineer and parse effectively. Not to mention the fact that companies change the source code of web pages rather often, so any example that I might make while I am writing this paragraph might break by the time you read this paragraph.
Though much less desirable, manual HTML parsing is still useful for a couple reasons. The arguments are separated by commas. The encoding of each argument follows directly how it is encoded in a.
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