Checking for a sequence in a python list

Question

I have a list [T20, T5, T10, T1, T2, T8, T16, T17, T9, T4, T12, T13, T18]

I have stripped out the T's, coverted to integer type and sorted the list to get this:

sorted_ids=[1, 2, 4, 5, 8, 9, 10, 12, 13, 16, 17, 18, 20]

I'm looping over the list and checking if the next number to current number is in numerical sequence. If not I want to insert a "V" in its position.

So eventually the list should look like: [1, 2, V, 4, 5, V, V, 8, 9, 10, V, 12, 13, V, V, 16, 17, 18, V, 20]

However, I'm not able to insert the exact no of V's at the right positions.

def arrange_tickets(tickets_list):

    ids=[]
    for item in tickets_list:
        new_str=item.strip("T")
        ids.append(int(new_str))
    sorted_ids = sorted(ids)
    temp_ids = []
    print("Sorted: ",sorted_ids)
    #size = len(sorted_ids)
    for i in range(len(sorted_ids)-1):
        temp_ids.append(sorted_ids[i])

        if sorted_ids[i]+1 != sorted_ids[i+1] :
            temp_ids.insert(i+1,"V")
    print(temp_ids)
    #print(sorted_ids)


tickets_list = ['T20', 'T5', 'T10', 'T1', 'T2', 'T8', 'T16', 'T17', 'T9', 'T4', 'T12', 'T13', 'T18']
print("Ticket ids of all the available students :")
print(tickets_list)
result=arrange_tickets(tickets_list)

Actual Result: [1, 2, 'V', 4, 'V', 5, 8, 'V', 9, 'V', 10, 12, 'V', 13, 16, 17, 18]

Expected Result: [T1, T2, V, T4, T5, V, V, T8, T9, T10, V, T12, T13, V, V, T16, T17, T18, V, T20]

Answer 1

Here is a solution:

sorted_ids=[1, 2, 4, 5, 8, 9, 10, 12, 13, 16, 17, 18, 20]

def arrange(inList):
    newList = []
    newList.append('T'+str(inList[0]))
    for i in range(1,len(inList)):
        diff = inList[i] - inList[i-1]
        if diff > 1:
            for d in range(diff-1):
                newList.append('V')
            newList.append('T'+str(inList[i]))
        else:
            newList.append('T'+str(inList[i]))
    return newList

print(arrange(sorted_ids))

Output:

['T1', 'T2', 'V', 'T4', 'T5', 'V', 'V', 'T8', 'T9', 'T10', 'V', 'T12', 'T13', 'V', 'V', 'T16', 'T17', 'T18', 'V', 'T20']

Answer 2

Here's another solution worth considering:

sorted_ids=[1, 2, 4, 5, 8, 9, 10, 12, 13, 16, 17, 18, 20]

for i in range(min(sorted_ids), max(sorted_ids)): 
     if sorted_ids[i] != i + 1: 
         sorted_ids.insert(i, 'V')

final_list = [ "T" + str(x) if isinstance(x, int) else x for x in sorted_ids]

result:

['T1', 'T2', 'V', 'T4', 'T5', 'V', 'V', 'T8', 'T9', 'T10', 'V', 'T12', 'T13', 'V', 'V', 'T16', 'T17', 'T18', 'V', 'T20']

Answer 3

Here is a list comprehension which gets you what you want:

sorted_ids=[1, 2, 4, 5, 8, 9, 10, 12, 13, 16, 17, 18, 20]
a = sorted_ids[0]
b = sorted_ids[-1]
nums = set(sorted_ids)
expected = ["T" + str(i) if i in nums else 'V' for i in range(a,b+1)]
print(expected)

Output:

['T1', 'T2', 'V', 'T4', 'T5', 'V', 'V', 'T8', 'T9', 'T10', 'V', 'T12', 'T13', 'V', 'V', 'T16', 'T17', 'T18', 'V', 'T20']

Answer 4

temp_ids.insert(i+1,"V") 

This is the troublesome statement. Update your code in following way

temp_ids=[]

for i in range(len(sorted_ids)-1):
    temp_ids.append(sorted_ids[i])

    if sorted_ids[i]+1 != sorted_ids[i+1] :
        for i in range(sorted_ids[i+1]-sorted_ids[i]-1):
            temp_ids.append("V") # appends as many V's as required

temp_ids.append(sorted_ids[-1]) # appends last element

This should work Suppose sorted array is [1,2,6]

So our desired output should be [1,2,'V','V','V',6]. So every time

sorted_ids[i]+1 != sorted_ids[i+1]

condition holds, we will have to append few numbers of V's. Now to determine how many V's we append, see that between 2 and 6 , 3 V's will be appended. So in general we append (sorted_ids[i+1] - sorted[i] -1) V's.

Now see this line

for i in range(len(sorted_ids)-1):

Because of this line, our list only runs for [1,2] in [1,2,6] , and we never append 6 in our For Loop, so after exiting For Loop it was appended.

Answer 5

First consider what ids should be in the list, assuming they start from 1 and end with the largest one present. Then check if each expected id is actually present, and if not put a "V" there. As a side-effect this also sorts the list.

def arrange_tickets(tickets_list):
    ids = [int(ticket[1:]) for ticket in tickets_list]
    expected_ids = range(1, max(ids) + 1)
    return ["T%d" % n if n in ids else "V" for n in expected_ids]

tickets_list = ['T20', 'T5', 'T10', 'T1', 'T2', 'T8', 'T16', 'T17', 'T9', 'T4', 'T12', 'T13', 'T18']
print("Ticket ids of all the available students :")
print(tickets_list)
result=arrange_tickets(tickets_list)
print(result)   

result:

Ticket ids of all the available students :
['T20', 'T5', 'T10', 'T1', 'T2', 'T8', 'T16', 'T17', 'T9', 'T4', 'T12', 'T13', 'T18']

['T1', 'T2', 'V', 'T4', 'T5', 'V', 'V', 'T8', 'T9', 'T10', 'V', 'T12', 'T13', 'V', 'V', 'T16', 'T17', 'T18', 'V', 'T20']

Answer 6

You can use this itertools recipe to first group consecutive numbers:

from itertools import groupby
from operator import itemgetter

def groupby_consecutive(lst):
    for _, g in groupby(enumerate(lst), lambda x: x[0] - x[1]):
        yield list(map(itemgetter(1), g))

sorted_ids = [1, 2, 4, 5, 8, 9, 10, 12, 13, 16, 17, 18, 20]
print(list(groupby_consecutive(lst=sorted_ids)))
# [[1, 2], [4, 5], [8, 9, 10], [12, 13], [16, 17, 18], [20]]

Then you can make a function that gets the interspersing V values from the previous groupings:

def interperse(lst):
    for x, y in zip(lst, lst[1:]):
        yield ["V"] * (y[0] - x[-1] - 1)

groups = list(groupby_consecutive(lst))
print(list(interperse(groups)))
# [['V'], ['V', 'V'], ['V'], ['V', 'V'], ['V']]

Then you can finally zip the above results together:

def add_prefix(lst, prefix):
    return [prefix + str(x) for x in lst]

def create_sequences(lst, prefix='T'):
    groups = list(groupby_consecutive(lst))
    between = list(interperse(groups))

    result = add_prefix(groups[0], prefix)
    for x, y in zip(between, groups[1:]):
        result.extend(x + add_prefix(y, prefix))

    return result

sorted_ids = [1, 2, 4, 5, 8, 9, 10, 12, 13, 16, 17, 18, 20]
print(create_sequences(lst=sorted_ids))
# ['T1', 'T2', 'V', 'T4', 'T5', 'V', 'V', 'T8', 'T9', 'T10', 'V', 'T12', 'T13', 'V', 'V', 'T16', 'T17', 'T18', 'V', 'T20']

Answer 7

In one shot, directly form the original array

array = ['T20', 'T5', 'T10', 'T1', 'T2', 'T8', 'T16', 'T17', 'T9', 'T4', 'T12', 'T13', 'T18']

You can define a method that does all the job:

def add_vs_between_not_cons(array):
  iterable = sorted(array, key= lambda x: int(x[1:]))
  i, size = 0, len(iterable)
  while i < size:
    delta = int(iterable[i][1:]) - int(iterable[i-1][1:])
    for _ in range(delta-1):
      yield "V"
    yield iterable[i]
    i += 1

So, you can call:

print(list(add_vs_between_not_cons(array)))

#=> ['T1', 'T2', 'V', 'T4', 'T5', 'V', 'V', 'T8', 'T9', 'T10', 'V', 'T12', 'T13', 'V', 'V', 'T16', 'T17', 'T18', 'V', 'T20']

Answer 8

my solution for infytq queries:

def arrange_tickets(tickets_list):
    ids = [int(ticket[1:]) for ticket in tickets_list]
    expected_ids = range(1, max(ids) + 1)
    listt=["T%d" % n if n in ids else "V" for n in expected_ids]
    list1=listt[0:10]
    list2=listt[11:]
    for i in range(10):
        if 'V' in list2:
            list2.remove('V')
    for j in range(0,len(list2)):
        for n, i in enumerate(list1):
            if i == 'V':
                list1[n] = list2[j]
                j+=1
    return list1
tickets_list = ['T5','T7','T1','T2','T8','T15','T17','T19','T6','T12','T13']
print("Ticket ids of all the available students :")
print(tickets_list)
result=arrange_tickets(tickets_list)
print()
print("Ticket ids of the ten students in Group-1:")
print(result[0:10])