Sum numbers by letter in list of tuples
<p>I have a list of tuples: </p>

<pre><code>[ ('A',100), ('B',50), ('A',50), ('B',20), ('C',10) ]
</code></pre>

<p>I am trying to sum up all numbers that have the same letter. I.e. I want to output </p>

<pre><code>[('A', 150), ('B', 70), ('C',10)] 
</code></pre>

<p>I have tried using set to get the unique values but then when I try and compare the first elements to the set I get </p>

<pre><code>TypeError: unsupported operand type(s) for +: 'int' and 'str'
</code></pre>

<p>Any quick solutions to match the numbers by letter?</p>

<p>Try this:</p>

<pre><code>a = [('A',100), ('B',50), ('A',50), ('B',20), ('C',10) ]

letters = set([s[0] for s in a])

new_a = []
for l in letters:
    nums = [s[1] for s in a if s[0] == l]
    new_a.append((l, sum(nums)))

print new_a    
</code></pre>

<p>Results:</p>

<pre><code>[('A', 150), ('C', 10), ('B', 70)]
</code></pre>

python list tuples