创建值是列表的字典

Question

I'm trying to create a dictionary containing lists, based on a 'lists [i] [1]' key.

lists = [['Col',1,5,9],
         ['Col',1,8,9],
         ['Col',2,1,9],
         ['Row',2,9,9],
         ['Row',2,7,8],
         ['Row',3,7,9],
         ['Row',3,6,9]]

dict_pis = {}
z_req_list = []
for i in range(len(lists)):

    if lists[i][0] == 'Row':

        key = lists[i][1]
        muv = lists[i][2]/lists[i][3]
        z_req = (muv / (0.9 * 25310506.54))*10000
#        z_req_list.append(z_req)
        dict_pis[key] = z_req
#        dict_pis[key] = z_req_list
        print(i+1,5*' ',key,5*' ', round(z_req,6))
print(dict_pis)
#        print(i+1,5*' ',key,5*' ', z_req_list)

So I should have something like this:

dict_pis = {2: [0.000439, 0.000384], 3: [0.000341, 0.000293]}

But what I get is the last value for each key, how can that be solved? I have tried to create an empty list to host my values by key, but it did not work for me.

I really appreciate the help, kind regards.

Answer 1

You can use a defaultdict orsetdefault() to create a list for a key by default. It will also be a little clearer if you don't use indices in the loop, but just loop over the items:

lists = [['Col',1,5,9],
         ['Col',1,8,9],
         ['Col',2,1,9],
         ['Row',2,9,9],
         ['Row',2,7,8],
         ['Row',3,7,9],
         ['Row',3,6,9]]

d = {}
for l in lists:
    kind, k, x, y = l
    if kind == "Row":
        d.setdefault(k, []).append(10000 * x / y / (0.9 * 25310506.54))

print(d)
# {2: [0.00043899204836345053, 0.00038411804231801923],
#  3: [0.0003414382598382393, 0.0002926613655756337]}

It's not clear from the question if you want the rounded values in the dict, but I think you know how to do that it you want it.

Answer 2

You have to check if there is list for current key and eventually create it

    if key not in dict_pis:
        dict_pis[key] = []

    dict_pis[key].append(z_req)

---

lists = [['Col',1,5,9],
         ['Col',1,8,9],
         ['Col',2,1,9],
         ['Row',2,9,9],
         ['Row',2,7,8],
         ['Row',3,7,9],
         ['Row',3,6,9]]

dict_pis = {}

for i in range(len(lists)):
    if lists[i][0] == 'Row':
        key = lists[i][1]
        muv = lists[i][2]/lists[i][3]

        z_req = (muv / (0.9 * 25310506.54))*10000

        if key not in dict_pis:
            dict_pis[key] = []

        dict_pis[key].append(z_req)

        print(i+1,5*' ',key,5*' ', round(z_req,6))

print(dict_pis)

Answer 3

Another solution with dictionary comprehension:

lists = [['Col',1,5,9],
         ['Col',1,8,9],
         ['Col',2,1,9],
         ['Row',2,9,9],
         ['Row',2,7,8],
         ['Row',3,7,9],
         ['Row',3,6,9]]

def z_req(x, y):
    """ Calculate z req """
    muv = x / y
    return (muv / (0.9 * 25310506.54))*10000

# create dictionary 
dic = { value[1] : [] for value in lists }

# append z_req results
for type, key, x, y in lists:
    if type == 'Row':
        dic[key].append(z_req(x, y))

Answer 4

Just for fun, in one dictionary comprehension;

def z_req(x, y):
    muv = x / y
    return (muv / (0.9 * 25310506.54))*10000

dic = { value[1] : [ z_req(v[2], v[3]) for v in lists \
                    if value[1] == v[1] and v[0] == 'Row' ] \
        for value in lists }

Although, you do have a problem with 1;

{1: [],
 2: [0.00043899204836345053, 0.00038411804231801923],
 3: [0.0003414382598382393, 0.00029266136557563367]}