Setting matrix table in Django

Question

I have two tables, in the example (any) of the figure below i have the table Paises and the table Energia

Setting a third table in Django I would have something with the fields

pais, energia, valor

Áustria, Carvão, 3.6

Áustria, Ciclo combinado de gás, 3.4

and so on.

Question: How I would mount this table in the template as it is in the image?

Edited:

@mgibsonbr I adapted to my model, see the code below.

def quotation_list(request):
    stores = list(Store.objects.all())
    products = list(Product.objects.all())
    # indice
    index_store = {store.id: index for index, store in enumerate(stores)}
    index_product = {product.id: index for index,
                     product in enumerate(products)}
    # dados para o template
    cabecalho = ["Lojas"] + [store.store for store in stores]
    linhas = [([product.product] + [None for store in stores])
              for product in products]

    for pev in Quotation.objects.all():
        linhas[index_store[pev.store_id]][
            index_product[pev.product_id]] = pev.price

But the following mistake.

Alias, how do I return the items in context to render on the page? return.

Answer 1

I would recommend treating your data on view before sending to template:

paises = list(Paises.objects.all())    # Filtre e ordene como achar melhor
energias = list(Energia.objects.all()) # idem

# Auxiliares
indices_pais = { pais.id:indice for indice,pais in enumerate(paises) }
indices_energia = { energia.id:indice for indice,energia in enumerate(energias) }

# Dados para o template
cabecalho = ["País"] + [energia.nome for energia in energias]
linhas = [( [pais.nome] + [None for energia in energias] ) for pais in paises]

for pev in PaisEnergia.objects.all(): # Filtre conforme os países e energias usados
    linhas[indices_pais[pev.pais_id]][indices_energia[pev.energia_id]+1] = pev.valor

Then you would send cabecalho and linhas to the template and render as a table. Note that if any country/energy is missing it will appear as None (you can customize this in creating linhas).

Example of how this could be rendered in a template:

<table>
    <thead>
        <tr>
        {% for item in cabecalho %}
            <th>{{ item }}</th>
        {% endfor %}
        </tr>
    </thead>
    <tbody>
    {% for linha in linhas %}
        <tr>
        {% for item in linha %}
            <td>{{ item }}</td>
        {% endfor %}
        </tr>
    {% endfor %}
    </tbody>
</table>

Remember that if you want to highlight the first column for example (the name of the country) you can do this using forloop.first, or maybe if you want the lines with alternating colors (for readability) can use forloop.counter, etc..

    {% for linha in linhas %}
        <tr class="{% if forloop.counter|divisibleby:2 %}cinza{% else %}azul{% endif %}">
        {% for item in linha %}
            <td{% if forloop.first %} class="bold"{% endif %}>{{ item }}</td>
        {% endfor %}
        </tr>
    {% endfor %}