# Better way to write algorithm, possibly recursive [closed]

I wrote the following code:

def find_storms_dst(d_f, max, min):
i = 0
storms = []
while i < len(d_f.index):
dst = d_f['Dst'][i]
if dst < max:
if dst < min:
print 'out of range'
s = Storm(i, d_f.index[i], dst)
while i < len(d_f.index)-1:
i += 1
dst = d_f['Dst'][i]
if dst < max:
if dst < min:
print 'out of range'
s.log(i, d_f.index[i], dst)
else:
break
storms.append(s)
i += 1
return storms


I does what I want. But I see some elements in it repeat, is that a recursion issue?

How one could write this better?

• You should add a description of what it is the code actually does. At the moment, we are left guessing. Dec 18, 2016 at 14:46
• "But I see some elements in it repeat, is that a recursion issue?" Does this code work the way that you want it to? Dec 18, 2016 at 16:10
• Recursion is when a method or function calls itself. I don't see that here. Perhaps in the larger code of which this is part. But if so, you should include that code as well. Dec 18, 2016 at 16:57

# Encapsulating checking the distance

You are checking whether dst < max and whether dst < min twice with the same consequences. By encapsulating this in a short function, you can avoid redundancies and make your code more clear. Assuming that min<max, this function would could look like this:

def check_dst(i):
dst = d_f['Dst'][i]
if dst < min:
print 'out of range'
return dst < max


As the above function only takes an index as an argument, it would have to be defined inside of find_storms_dst. This has more advantages in the following steps. Even if the following steps will reduce the need for using this function twice, it still makes your code more readable (and facilitates list filtering).

Moreover, it seems likely to me that you want to do something else if dst < min, e.g., raising an error or at least a warning and check_dst should not return True.

# Filtering first

Your code seems to do two things:

• Finding indices from your dst object that complies with certain criteria.

• Doing something with those indices that do comply.

By unnecessarily intertwining those aspects, you are complicating your code. So, let’s first find the indices that comply with your criteria and call them protostorms. With the above definition, this is pretty straightforward:

protostorms = filter(check_dst, range(len(d_f.index)))


# Compiling the proto-storms

Now, all that remains to do is to compile the list of storms from the proto-storms. An straightforward way to do this would be popping items from your protostorms list successively like this:

storms = []
while protostorms:
i = protostorms.pop(0)
s = Storm(i, d_f.index[i], d_f['Dst'][i])

while protostorms and protostorms[0]==i+1:
i = protostorms.pop(0)
s.log(i, d_f.index[i], dst)

storms.append(s)

return storms


# Result

Taking all of the above together, your new code would look like this:

def find_storms_dst(d_f, max, min):
def check_dst(i):
dst = d_f['Dst'][i]
if dst < min:
print 'out of range'
return dst < max

protostorms = filter(check_dst, range(len(d_f.index)))

storms = []
while protostorms:
i = protostorms.pop(0)
s = Storm(i, d_f.index[i], d_f['Dst'][i])

while protostorms and protostorms[0]==i+1:
i = protostorms.pop(0)
s.log(i, d_f.index[i], dst)

storms.append(s)

return storms


You could encapsulate the last loop, but I will leave it like this for now.

# Restructuring d_f and Storm

Another issue I noticed is that your d_f object seems to be structured in a cumbersome manner. To get a distance, you first have to get an index from d_f.index (by the way: Shouldn’t this be named d_f.indices?), which you then have to feed into d_f['Dst']. Also Storm and log take multiple properties from some element of d_f, which could be streamlined.

If you can, I recommend changing d_f such that it is an iterable of objects – let’s call them events –, which are accepted as an input by Storm and log and have an index and a distance as properties. Your code could then look like something along the line of the following:

def find_storms_dst(d_f, max, min):
def check_dst(event):
if event.dst < min:
print 'out of range'
return event.dst < max