I've two data sets in array:

arr1 = [['2011-10-10', 1, 1],['2007-08-09', 5, 3],...
]arr2 = [['2011-10-10', 3, 4],['2007-09-05', 1, 1],...
]

I want to combine them into one array like this:

arr3 = [['2011-10-10', 1, 1, 3, 4],...
]

I mean, just combine those lines with the same date column.

Just for clarification, I don't need those lines which not appear in both array, just drop them.

Organize your data differently (you can easily convert what you already have to two dicts):

d1 = { '2011-10-10': [1, 1],'2007-08-09': [5, 3]}
d2 = { '2011-10-10': [3, 4],'2007-09-05': [1, 1]}

Then:

d3 = { k : d1[k] + d2[k] for k in d1 if k in d2 }