diff -r 40657f9a4e4a -r 663c2a9108d1 pre_templates2/docdiff.scala
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/pre_templates2/docdiff.scala	Sun Nov 01 01:21:31 2020 +0000
@@ -0,0 +1,115 @@
+// Preliminary Part about Code Similarity
+//========================================
+
+
+object CW7a { 
+
+
+//(1) Complete the clean function below. It should find
+//    all words in a string using the regular expression
+//    \w+  and the library function 
+//
+//         some_regex.findAllIn(some_string)
+//
+//    The words should be Returned as a list of strings.
+
+
+def clean(s: String) : List[String] = ???
+  
+
+
+//(2) The function occurrences calculates the number of times  
+//    strings occur in a list of strings. These occurrences should 
+//    be calculated as a Map from strings to integers.
+
+
+def occurrences(xs: List[String]): Map[String, Int] = ???
+
+
+//(3) This functions calculates the dot-product of two documents
+//    (list of strings). For this it calculates the occurrence
+//    maps from (2) and then multiplies the corresponding occurrences. 
+//    If a string does not occur in a document, the product is zero.
+//    The function finally sums up all products. 
+
+
+def prod(lst1: List[String], lst2: List[String]) : Int = ???
+
+
+//(4) Complete the functions overlap and similarity. The overlap of
+//    two documents is calculated by the formula given in the assignment
+//    description. The similarity of two strings is given by the overlap
+//    of the cleaned strings (see (1)).  
+
+
+def overlap(lst1: List[String], lst2: List[String]) : Double = ???
+
+def similarity(s1: String, s2: String) : Double = ???
+
+
+
+/* Test cases
+
+
+val list1 = List("a", "b", "b", "c", "d") 
+val list2 = List("d", "b", "d", "b", "d")
+
+occurrences(List("a", "b", "b", "c", "d"))   // Map(a -> 1, b -> 2, c -> 1, d -> 1)
+occurrences(List("d", "b", "d", "b", "d"))   // Map(d -> 3, b -> 2)
+
+prod(list1,list2) // 7 
+
+overlap(list1, list2)   // 0.5384615384615384
+overlap(list2, list1)   // 0.5384615384615384
+overlap(list1, list1)   // 1.0
+overlap(list2, list2)   // 1.0
+
+// Plagiarism examples from 
+// https://desales.libguides.com/avoidingplagiarism/examples
+
+val orig1 = """There is a strong market demand for eco-tourism in
+Australia. Its rich and diverse natural heritage ensures Australia's
+capacity to attract international ecotourists and gives Australia a
+comparative advantage in the highly competitive tourism industry."""
+
+val plag1 = """There is a high market demand for eco-tourism in
+Australia. Australia has a comparative advantage in the highly
+competitive tourism industry due to its rich and varied natural
+heritage which ensures Australia's capacity to attract international
+ecotourists."""
+
+similarity(orig1, plag1) // 0.8679245283018868
+
+
+// Plagiarism examples from 
+// https://www.utc.edu/library/help/tutorials/plagiarism/examples-of-plagiarism.php
+
+val orig2 = """No oil spill is entirely benign. Depending on timing and
+location, even a relatively minor spill can cause significant harm to
+individual organisms and entire populations. Oil spills can cause
+impacts over a range of time scales, from days to years, or even
+decades for certain spills. Impacts are typically divided into acute
+(short-term) and chronic (long-term) effects. Both types are part of a
+complicated and often controversial equation that is addressed after
+an oil spill: ecosystem recovery."""
+
+val plag2 = """There is no such thing as a "good" oil spill. If the
+time and place are just right, even a small oil spill can cause damage
+to sensitive ecosystems. Further, spills can cause harm days, months,
+years, or even decades after they occur. Because of this, spills are
+usually broken into short-term (acute) and long-term (chronic)
+effects. Both of these types of harm must be addressed in ecosystem
+recovery: a controversial tactic that is often implemented immediately
+following an oil spill."""
+
+overlap(clean(orig2), clean(plag2))  // 0.728
+similarity(orig2, plag2)             // 0.728
+
+
+ 
+// The punchline: everything above 0.6 looks suspicious and 
+// should be investigated by staff.
+
+*/
+
+}