Alexzive wrote:
Hello there,let's suppose I have the following matrix: mat = [[1,2,3], [3,2,4], [7,8,9], [6,2,9]] where [.. , .. , ..] are the rows. I am interested into getting the "row index" of all the matrix rows where a certain number occurs. For example for 9 I should get 2 and 3 (starting from 0). For 10 I should get an error msg (item not found) and handle it. How to get the"row indexes" of found items? In practice I am looking for an equivalent to "list.index(x)" for the case "lists of lists"
Actually you are not ;) list.index(x) gives you the index of the first occurence of the item. So what you seem to want is a list of indexes to the lists where your item is contained. Something like: x=9 [idx for idx,row in enumerate(mat) if x in row] should do.
PS: this is just a simplified example, but I have actually to deal with large matrices [~500000 * 4]
This is something I'd consider either reordering your data (for example into dictionary) or look at scipy/numpy. Regards Tino
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