Python: Output format of a list

Question

I have a list of temperatur measurement:

temp = [ [39, 38.5, 38], [37,37.5, 36], [35,34.5, 34], [33,32.5, 32], [31,30.5, 30], [29,28.5, 28], [27,26.5,26] ]

every value is recorded every 5 hour over several days. First day is first list of temp: [39, 38.5, 38], second day is second list of temp: [37, 37.5, 36] etc.

What I always do is, I loop over the 'temp' and calculate the time difference between the values and save this as list in time. (The time difference is always 5h)

time=[]
for t in temp:
 for i,val in enumerate(t):
         i=i*5
         time.append(i)
print time

The output looks like this:

time: [0, 5, 10, 0, 5, 10, 0, 5, 10, 0, 5, 10, 0, 5, 10, 0, 5, 10, 0, 5, 10]

But I want to get sublists of every day, like:

time: [ [0, 5, 10] , [0, 5, 10], [0, 5, 10], [0, 5, 10], [0, 5, 10], [0, 5, 10], [0, 5, 10] ]

What`s wrong in my code?

Answer 1

You keep appending to the same list, you should create a new list for every day.

time=[]
for t in temp:
    day_list = [] # Create a new list
    for i,val in enumerate(t):
        i=i*5
        day_list.append(i) # Append to that list
    time.append(day_list) # Then append the new list to the output list
print time

For a list comprehension:

time = [[i*5 for i, val in enumerate(t)] for t in temp]

Answer 2

You are appending all timestamp to a single-level list, so that's what your algorithm outputs.

Here is one way to get a list of lists:

>>> [list(range(0, len(t) * 5, 5)) for t in temp]
[[0, 5, 10], [0, 5, 10], [0, 5, 10], [0, 5, 10], [0, 5, 10], [0, 5, 10], [0, 5, 10]]

This correctly deals with sublists of temp potentially having different lengths.

Answer 3

If you want the exact same thing in each list, do this:

time = [[0,5,10] for _ in temp]

To account for variable sublist length:

In python 2

time = [range(0, len(i)*5, 5) for i in temp]

In python 3, must materialize range:

time = [list(range(0, len(i)*5, 5)) for i in temp]

Answer 4

You have to create a temporary sub list and then append that sublist to the actual list to get a bunch of sublists within a list

temp = [ [39, 38.5, 38], [37,37.5, 36], [35,34.5, 34], [33,32.5, 32], [31,30.5, 30], [29,28.5, 28], [27,26.5,26] ]
time=[]
for t in temp:
    l = []
    for i,val in enumerate(t):
        i=i*5
        l.append(i)
        if len(l) == 3:
            time.append(l)
print time

Answer 5

使用列表理解，您可以在一行中完成：

time = [[i*5 for i, val in enumerate(t)] for t in temp]