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Algorithms: Sorting and Searching

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Sorting Names

1:59 with Jay McGavren

Before we can use the Binary Search algorithm on our list of names, we need to sort it. Let's do that now. We need to load our unsorted list of names from a file, sort it, and write the sorted names back out to a new file.

Before we can use the Binary Search algorithm on our list of names, we need to sort it. Let's do that now. We need to load our unsorted list of names from a file, sort it, and write the sorted names back out to a new file.

# Again, this code at the top just loads a file full of strings into a list.
import sys
from load import load_strings

names = load_strings(sys.argv[1])

# We'll use our quicksort method to sort the list of names. Its code is
# completely unchanged from when you saw it in the previous stage.
def quicksort(values):
  if len(values) <= 1:
    return values
  less_than_pivot = []
  greater_than_pivot = []
  pivot = values[0]
  for value in values[1:]:
    if value <= pivot:
      less_than_pivot.append(value)
    else:
      greater_than_pivot.append(value)
  return quicksort(less_than_pivot) + [pivot] + quicksort(greater_than_pivot)

# We just call our quicksort function on the list of names loaded from the
# file, and save the list to a variable.
sorted_names = quicksort(names)
# Then, we loop through each name in the sorted list...
for n in sorted_names:
  # ...And print that name.
  print(n)
  • That's all there is to it! Let's try running this script.
python quicksort_strings.py names/unsorted.txt
  • That prints the sorted list of names out to the terminal. But we need it in a file.
  • So we'll do what's called a redirect of the program's output.
  • We'll run the same command as before, but at the end we'll put a > greater than sign, followed by the path to a file that we want the program output written to: names/sorted.txt
  • Redirecting works not only on Linux-based systems like Workspaces, but also on Macs and even on Windows machines. You just need to be careful because if you redirect to an existing file, its contents will be overwritten without asking you.
python quicksort_strings.py names/unsorted.txt > names/sorted.txt

Now we can load this file of sorted names into a list, and we'll be able to use that list with the Binary Search algorithm. We'll see how to do that next.

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    Before we can use the binary search algorithm on our list of names, 0:00
    we need to sort it. 0:04
    Let's do that now. 0:05
    We need to load our unsorted list of names from a file, sort it, and 0:06
    write the sorted names back out to a new file. 0:10
    Again, this code at the top just loads a file full of strings into a list. 0:12
    We'll use our quicksort method to sort the list of names. 0:17
    Its code is completely unchanged from when you saw it in the previous stage. 0:20
    We just call our quicksort function on the list of names loaded from the file and 0:24
    save the list to a variable. 0:28
    Then we loop through each name in the sorted list, And we print that name. 0:32
    That's all there is to it. 0:39
    Let's save this script and try running it. 0:40
    python quicksort_strings.py and 0:43
    we'll pass it the names/unsorted.text file. 0:47
    Resize the console window here a little bit. 0:53
    That prints the sorted list of names out to the terminal, but we need it in a file. 0:59
    So we'll do what's called a redirect of the program's output. 1:04
    We'll run the same command as before. 1:07
    But at the end, we'll put a greater than sign, followed by the path to a file that 1:09
    we want the program output written to, names/sorted.text. 1:13
    Redirecting works not only on Linux-based systems like WorkSpaces, 1:22
    but also on Macs and even on Windows machines. 1:26
    You just need to be careful because if you redirect to an existing file, 1:28
    its contents will be overwritten without asking you. 1:32
    Let me refresh the list of files in the sidebar. 1:35
    And you'll see that we now have a new sorted.txt file in the names directory. 1:40
    It's the same number of lines as the unsorted.txt file, but 1:45
    all the names are sorted now. 1:49
    Now we can load this file of sorted names into a list, and 1:51
    we'll be able to use that list with binary search algorithm. 1:53
    We'll see how to do that next. 1:57

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