Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Both sides previous revision Previous revision
Next revision 		Previous revision
lfa:lab01-python-intro [2021/09/14 09:40]
pdmatei 		lfa:lab01-python-intro [2021/10/07 11:32] (current)
ioana.georgescu [List comprehensions]
Line 45: Line 45:
 l[:x] l[:x]
 # the last element of a list: # the last element of a list:
-l[:-1]+l[-1]
 # the last three elements of a list: # the last three elements of a list:
-l[:-3]+l[-3:]
 # the slice from n-3 to n-1, where n is the number of elements from the list # the slice from n-3 to n-1, where n is the number of elements from the list
 l[-3:-1] l[-3:-1]
Line 197: Line 197:
     ​     ​
     # computing the average ages (a map could have also been used)     # computing the average ages (a map could have also been used)
-    avg = reduce(lambda a,b:a+b, [age(x) for x in l]) / len(l)+    avg = reduce(lambda a,b:a+b, [age(x[-1]) for x in l]) / len(l)
     ​     ​
     # we return the last name and the age of the filtered list l     # we return the last name and the age of the filtered list l
Line 281: Line 281:
  
 */ */
 +
 +===== Practice =====
 +
 +A labelled graph is encoded as a file where:
 +  * **the first line** consists of the number of nodes
 +  * **each subsequent line** is an edge ''<​from>​ <​label>​ <​to>''​
 +Example:
 +<​code>​
 +5
 +0 X 1
 +1 O 2 
 +1 X 3
 +1 O 4
 +4 X 1
 +3 O 2
 +</​code>​
 +
 +  * Suppose we encode streets as labelled graphs, where each label '​X'​ or '​O'​ denotes if a street is closed or open. 
 +  * Compute the set of accessible nodes from a given **source**, via open streets.
 +  * (Hint1: google //Python read lines// to see how to read from a file; also, google ''​split''​ in Python)
 +  * (Hint2: you will need a dictionary to store, for each node and label l, the list of its l-successors)
 +
 +
 +===== Haskell practice =====
 +
 +Solve the same exercise, only build your own input as a string, instead of a file.