.NET/Java PDF, Tiff, Barcode SDK Library

When working with strings at an advanced level, it becomes necessary to learn about regular expressions. A regular expression is, essentially, a search query, and not to be confused with the expressions we ve discussed already in this chapter. If you type ruby into your favorite search engine, you d expect information about Ruby to appear. Likewise, if your regular expression is ruby and you run that query against, say, a long string, you d

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To color-code these slides in Slide Sorter view, click Ctrl+A to select all the slides in the presentation. On the Home tab, in the Slides group, click Layout, and on the drop-down menu, click the layout titled Detail Sketches, as shown in Figure 6-5. Now apply the rest

expect any matches to be returned. A regular expression, therefore, is a string that describes a pattern for matching elements in other strings.

Note This section provides only a brief introduction to regular expressions. Regular expressions are a

Tip If you want a First-In, First-Out (FIFO) queue, you can use insert(0, ...) instead of append. Alternatively, you could keep using append but substitute pop(0) for pop(). An even better solution would be to use a deque from the collections module. See 10 for more information.

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major branch of computer science, and many books and Web sites are dedicated to their use. Ruby supports the majority of standard regular expression syntax, so non Ruby-specific knowledge about regular expressions obtained from elsewhere can still prove useful in Ruby.

One thing you ll often want to do is substitute something within a string for something else. Take this example:

of the layouts in the order of the informational hierarchy of your slides, from top to bottom. Select the Call to Action slide, click Layout, and on the drop-down menu, click the layout titled CTA Sketch. Next select the rst Key Point slide, hold down Ctrl and click to select the second and third Key Point slides, and then click Layout again, and on the drop-down menu, click the layout titled Key Point Sketches.

puts "foobar".sub('bar', 'foo')

In this example you use a method on the string called sub, which substitutes the first instance of the first parameter 'bar' with the second parameter 'foo', resulting in foofoo. sub only does one substitution at a time, on the first instance of the text to match, whereas gsub does multiple substitutions at once, as this example demonstrates:

The remove method is used to remove the first occurrence of a value: >>> x = ['to', 'be', 'or', 'not', 'to', 'be'] >>> x.remove('be') >>> x ['to', 'or', 'not', 'to', 'be'] >>> x.remove('bee') Traceback (innermost last): File "<pyshell#3>", line 1, in x.remove('bee') ValueError: list.remove(x): x not in list As you can see, only the first occurrence is removed, and you cannot remove something (in this case, the string 'bee') if it isn t in the list to begin with. It s important to note that this is one of the nonreturning in-place changing methods. It modifies the list, but returns nothing (as opposed to pop).

FIGURE 6-5 Applying the Detail Sketches custom layout to all the slides in Slide Sorter view using the

puts "this is a test".gsub('i', '')

Here you ve substituted all occurrences of the letter 'i' with an empty string. What about more complex patterns Simply matching the letter 'i' is not a true example of a regular expression. For example, let s say you want to replace the first two characters of a string with 'Hello':

x = "This is a test" puts x.sub(/^../, 'Hello')

Next click the rst Explanation slide, hold down Ctrl and select the rest of the Explanation slides, and then click the Layout button, and on the drop-down menu click the layout titled Explanation Sketches. Last click the rst Setting slide, hold down Shift and select the Point B slide, and then click the Layout button, and on the drop-down menu click the layout titled Act I Sketches.

The reverse method reverses the elements in the list. (Not very surprising, I guess.) >>> >>> >>> [3, x = [1, 2, 3] x.reverse() x 2, 1]