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Jorge Ponti
Asked: 2020-07-19 06:17:49 +0800 CST 2020-07-19 06:17:49 +0800 CST

Sum elements contained in a Python dictionary

  • 772

I need to create a dictionary that has the sum of elements of another dictionary, in the most computationally efficient way.

The main dictionary is of the form:

{'11': [0.76700000000000002, 3455.0, 0.76700000000000002, 0.76700000000000002, 34.0, 0.76700000000000002], '22': [34.0, 0.76700000000000002]}

I need to create a new dictionary containing the same keys but with the sum of the integers from the first dictionary. The output would then be:

{'11': [3458], '22': [34.767]}
python

2 Answers

  1. Best Answer

    If you want to create a new dictionary (not do the addition on the one you already have) the simplest and most efficient thing to do is to use compression dictionaries together with the built-in function sum:

    d = {'11': [0.76700000000000002, 3455.0, 0.76700000000000002,
            0.76700000000000002, 34.0, 0.76700000000000002],
     '22': [34.0, 0.76700000000000002]}

    • In Python 3:

      r = {key: [sum(value)] for key, value in d.items()}

    • In Python 2:

      r = {key: [sum(value)] for key, value in d.iteritems()}

    The output is:

    {'11': [3492.0679999999993], '22': [34.767]}

    The reason to use dict.iteritemsin Python 2 is because it dict.itemsreturns a list of key/value tuples in this version, which can result in memory and efficiency issues with large dictionaries. iteritemsreturns an iterator. In Python 3, it dict.itemsreturns a view object , which is iterable.

    If you want to avoid precision errors caused by intermediate sums and their floating-point representation as much as possible, you can use math.fsum:

    • Python 3:

      import math

r = {key: [math.fsum(value)] for key, value in d.items()}

    • Python 2:

      import math

r = {key: [math.fsum(value)] for key, value in d.iteritems()}

    Departure:

    {'11': [3492.068], '22': [34.767]}

    Since you are creating a list with only one element, if you are not going to use that list later, create the keys with the sum only:

    r = {key: math.fsum(value) for key, value in d.items()}

    Departure:

    {'11': 3492.068, '22': 34.767}

    • 5

  2. what you have to do is iterate through the dictionary and on each element iterate through the list and add it

    main_dic = {'11': [0.7670, 3455, 0.767, 0.767, 34.0, 0.767], '22': [34.0, 0.767]}
dic_result = {}
for key, value in main_dic.items(): # iterar los item del diccionario
    suma = 0 # variable donde se guardará la suma de los elementos
    for v in value: # iterar los elementos
        suma += v # sumar los elementos y guardarlos
    dic_result[key] = suma # añadir al nuevo diccionario la misma llave con la suma de los elementos

    or if you prefer this in a function:

        def suma_valores_dic(main_dic):
        dic_result = {}
        for key, value in main_dic.items():
            suma = 0
            for v in value:
                suma += v
            dic_result[key] = suma
        return dic_result

    then just call the function:

    diccionario = {'11': [0.7670, 3455, 0.767, 0.767, 34.0, 0.767], '22': [34.0, 0.767]}
resultado = suma_valores_dic(diccionario)
print(resultado)

    For more information on the use of dictionaries, I have found some documentation that may be of use to you:

    1. https://jarroba.com/dictionary-python-examples/
    2. http://librosweb.es/libro/algoritmos_python/capitulo_9/using_dictionaries_en_python.html especially in webbooks , there is a lot of information that can help you. Also his Python session for beginners
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