possible_list = []
bigger_list = []
new_list= [0, 25, 2, 1, 14, 1, 14, 1, 4, 6, 6, 7, 0, 10, 11]
for i in range(0,len(new_list)):
# if the next index is not greater than the length of the list
if (i + 1) < (len(new_list)):
#if the current value is less than the next value
if new_list[i] <= new_list[i+1]:
# add the current value to this sublist
possible_list.append(new_list[i])
# if the current value is greater than the next, close the list and append it to the lager list
bigger_list.append(possible_list)
print bigger_list
How do I find the longest consistent increment in the list called new_list?
I expect the result to be
[[0,2], [2], [1,14], [1,14], [1,4,6,6,7], [0,10,11]]
I can find the remaining solution from there myself.
One problem (but not the only one) with your code is that you are always adding the elements to the same possible_list, thus the lists in bigger_list are in fact all the same list!
Instead, I suggest using [-1] to access the last element of the list of subsequences (i.e. the one to append to) and [-1][-1] to access the last element of that subsequence (for comparing the current element to).
new_list= [0, 25, 2, 1, 14, 1, 14, 1, 4, 6, 6, 7, 0, 10, 11]
subseq = [[]]
for e in new_list:
if not subseq[-1] or subseq[-1][-1] <= e:
subseq[-1].append(e)
else:
subseq.append([e])
This way, subseq ends up the way you want it, and you can use max to get the longest one.
>>> subseq
[[0, 25], [2], [1, 14], [1, 14], [1, 4, 6, 6, 7], [0, 10, 11]]
>>> max(subseq, key=len)
[1, 4, 6, 6, 7]
Related
I'm trying to make a program that for a sublist of numbers, uses index as a variable and selects each number from the list of lists
so if my numbest = [[1, 2, 3, 4, 5], [2, 4, 6, 8, 10], [3, 5, 7, 9, 11]]
I want to be able to call the function like this
column_sum(2, [[1, 2, 3, 4, 5], [2, 4, 6, 8, 10], [3, 5, 7, 9, 11]]) will add the numbers at index 2 in each sublist (3, 6, and 7) and will return the number 16."
I can't for the life of me figure out how to print
for i in numlist:
print numbest[index]
Looks like Python, so imma say that all you need to do is have a variable that is a running total, add up all the numbers that are the values at the index you specify, and then return that value.
Alexander is also right and if his way is easier for you, you can find resources https://www.w3schools.com/python/ref_func_sum.asp and https://www.w3schools.com/python/python_lists_comprehension.asp
I use Maxima CAS to create the list:
a:makelist(i,i,1,20);
result:
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]
I want to slim the list and leave only every third element. To find it I check index i of the list a :
mod(i,3)>0
to find elements.
My code :
l:length(a);
for i:1 thru l step 1 do if (mod(i,3)>0) then a:delete(a[i],a);
Of course it does not work because length of a is changing.
I can do it using second list:
b:[];
for i:1 thru l step 1 do if (mod(i,3)=0) then b:cons(a[i],b);
Is it the best method ?
There are different ways to solve this, as know already. My advice is to construct a list of the indices you want to keep, and then construct the list of elements from that. E.g.:
(%i1) a:makelist(i,i,1,20);
(%o1) [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]
(%i2) ii : sublist (a, lambda ([a1], mod(a1, 3) = 0));
(%o2) [3, 6, 9, 12, 15, 18]
(%i3) makelist (a[i], i, ii);
(%o3) [3, 6, 9, 12, 15, 18]
The key part is the last step, makelist(a[i], i, ii), where ii is the list of indices you want to select. ii might be constructed in various ways. Here is a different way to construct the list of indices:
(%i4) ii : makelist (3*i, i, 1, 6);
(%o4) [3, 6, 9, 12, 15, 18]
One simple way (I do not know which one is best or faster) with compact code: makelist(a[3*i],i,1,length(a)/3)
Test example:
l1:makelist(i,i,1,12)$
l2:makelist(i,i,1,14)$
l3:[2,3,5,7,11,13,17,19,23,29]$
for a in [l1,l2,l3] do (
b:makelist(a[3*i],i,1,length(a)/3),
print(a,"=>",b)
)$
Result:
[1,2,3,4,5,6,7,8,9,10,11,12] => [3,6,9,12]
[1,2,3,4,5,6,7,8,9,10,11,12,13,14] => [3,6,9,12]
[2,3,5,7,11,13,17,19,23,29] => [5,13,23]
I am looking for a fast implementation of the following code; using, for instance, map() or next():
l = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
total_so_far = 0
for i in l:
total_so_far += i
if total_so_far > 14:
break
print(i)
The code prints the index of item in list where sum of start of list to the index is greater greater than 14.
Note: I need to continuously update the link in another loop. Therefore, a solution in numpy would probably be too slow, because it cannot update a list in-place.
You can also make use of itertools.accumulate() together with enumerate() and next():
In [1]: from itertools import takewhile
In [2]: l = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
In [3]: next(index for index, value in enumerate(accumulate(l)) if value > 14)
Out[3]: 5
Basically, wanted to iterate over a list of numerical data to change it's contents, where the numerical at the start of the list is moved to the last, and then the data is shifted to the left. Whilst I have achieved this, as the printed contents of the loop gives the desired results, when trying to append the contents of said loop to said dictionary, it only does this for the final iteration. Here's my code:
minor=[1,2,3,4,5,6]
MNP = {'scale degree' : []
}
def patterns(scale):
for i in scale:
print (scale)
scale.insert(len(scale),scale[0])
del(scale[0])
MNP['scale degree'].append(scale)
using the function patterns, this is the output:
>>> patterns(minor)
the list, minor, is at the top of the page by the way.
output:
[1, 2, 3, 4, 5, 6]
[2, 3, 4, 5, 6, 1]
[3, 4, 5, 6, 1, 2]
[4, 5, 6, 1, 2, 3]
[5, 6, 1, 2, 3, 4]
[6, 1, 2, 3, 4, 5]
Yet when I try to print the contents of the list, scale degree, in the MNP dict, the result is:
MNP['scale degree']
[[1, 2, 3, 4, 5, 6], [1, 2, 3, 4, 5, 6], [1, 2, 3, 4, 5, 6], [1, 2, 3, 4, 5, 6], [1, 2, 3, 4, 5, 6], [1, 2, 3, 4, 5, 6]]
I am very perplexed by this result, it's as if the output changes depending on the operation called upon it?
Thank you for any help in advance. It's also worth noting that I've been stuck with this for a good amount of time, so if there's any resources out there that may help me understand similar occurrences i certainly wouldn't pass that up.
The reason this happens is because what you store in MNP['scale degree'] is only a reference to scale. So when you change scale, so do the entries in MNP['scale degree']. What you need to do to avoid this is copying scale each time you append it (i.e. creating a new list instead of adding a reference). You can do this with the copy module:
import copy
minor=[1,2,3,4,5,6]
MNP = {'scale degree' : []
}
def patterns(scale):
for i in scale:
print (scale)
scale.insert(len(scale),scale[0])
del(scale[0])
MNP['scale degree'].append(copy.copy(scale))
patterns(minor)
print(MNP['scale degree'])
So I've been playing around with python and noticed something that seems a bit odd. The semantics of -1 in selecting from a list don't seem to be consistent.
So I have a list of numbers
ls = range(1000)
The last element of the list if of course ls[-1] but if I take a sublist of that so that I get everything from say the midpoint to the end I would do
ls[500:-1]
but this does not give me a list containing the last element in the list, but instead a list containing everything UP TO the last element. However if I do
ls[0:10]
I get a list containing also the tenth element (so the selector ought to be inclusive), why then does it not work for -1.
I can of course do ls[500:] or ls[500:len(ls)] (which would be silly). I was just wondering what the deal with -1 was, I realise that I don't need it there.
In list[first:last], last is not included.
The 10th element is ls[9], in ls[0:10] there isn't ls[10].
If you want to get a sub list including the last element, you leave blank after colon:
>>> ll=range(10)
>>> ll
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> ll[5:]
[5, 6, 7, 8, 9]
>>> ll[:]
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
I get consistent behaviour for both instances:
>>> ls[0:10]
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> ls[10:-1]
[10, 11, 12, 13, 14, 15, 16, 17, 18]
Note, though, that tenth element of the list is at index 9, since the list is 0-indexed. That might be where your hang-up is.
In other words, [0:10] doesn't go from index 0-10, it effectively goes from 0 to the tenth element (which gets you indexes 0-9, since the 10 is not inclusive at the end of the slice).
It seems pretty consistent to me; positive indices are also non-inclusive. I think you're doing it wrong. Remembering that range() is also non-inclusive, and that Python arrays are 0-indexed, here's a sample python session to illustrate:
>>> d = range(10)
>>> d
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> d[9]
9
>>> d[-1]
9
>>> d[0:9]
[0, 1, 2, 3, 4, 5, 6, 7, 8]
>>> d[0:-1]
[0, 1, 2, 3, 4, 5, 6, 7, 8]
>>> len(d)
10
when slicing an array;
ls[y:x]
takes the slice from element y upto and but not including x. when you use the negative indexing it is equivalent to using
ls[y:-1] == ls[y:len(ls)-1]
so it so the slice would be upto the last element, but it wouldn't include it (as per the slice)
-1 isn't special in the sense that the sequence is read backwards, it rather wraps around the ends. Such that minus one means zero minus one, exclusive (and, for a positive step value, the sequence is read "from left to right".
so for i = [1, 2, 3, 4], i[2:-1] means from item two to the beginning minus one (or, 'around to the end'), which results in [3].
The -1th element, or element 0 backwards 1 is the last 4, but since it's exclusive, we get 3.
I hope this is somewhat understandable.