Search a 2 dimensional python list for last occurrence in a particular column

Question

I have a list with [vehicle name, number]

a=[["car","A1"],["car","A2"],["truck","A1"]]

I need a function such that if i specify

car it should return "A2" the last number in that vehicle name. If i specify bike it should return "A0"

I tried writing something but keep getting an error list index out of range

EDIT:

here's the full list format

["vehicle","color","vehicle_num","status(True/False)","code"]

vehicle and color is given and last vehicle_num should be found, if vehicle,color doesn't exist return "A0"

The number system starts from "A1",.........."An"

n varies according to the vehicle,color

list is already sorted

Your job would be easier and efficient if you used a dictionary. — Keyur Potdar, Jun 06 '18 at 07:18

jpp · Answer 1 · 2018-06-06T08:50:15.353

2

Use a dictionary

You can take advantage of the fact dict assigns values in order and list is an ordered collection. So, for duplicate keys within your list of lists, the last mapping persists.

a = [["car","A1"], ["car","A2"], ["truck","A1"]]

d = dict(a)

print(d['car'])    # A2
print(d['truck'])  # A1

Revert to list if you need to afterwards (which you don't, as you can write to csv from a dictionary).

res = list(map(list, d.items()))

print(res)

[['car', 'A2'], ['truck', 'A1']]

edited Jun 06 '18 at 08:50

answered Jun 06 '18 at 08:10

jpp

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I need it to be a list because i store it in a csv file later – Noel DSouza Jun 06 '18 at 08:48
how would you use a dictionary for the edited part of the question? – Noel DSouza Jun 06 '18 at 09:08
1

`res = list(map(list, d.items()))`. Here, `d` is the dictionary from the first part. We convert dictionary key-value pairs, as demonstrated, to a list of lists. – jpp Jun 06 '18 at 09:09
how would you store this in a dictionary `["vehicle","color","vehicle_num","status(True/False)","code"]` – Noel DSouza Jun 06 '18 at 09:11
@NoelDSouza, For your new requirement, you should ask a new question with a **[mcve]**. – jpp Jun 06 '18 at 09:16

score 0 · Answer 2 · answered Jun 06 '18 at 09:14

0

You can use something like this:

def search(l, word):
    res = "A0"
    for i in l:
        if i[0] == word:
            res
    return res

You can then optimise it by saving "An" as Tupel of A with an integer n.

answered Jun 06 '18 at 09:14

Ludwig Austermann

1
2

score -1 · Answer 3 · answered Jun 06 '18 at 07:22

-1

a = {'car':['A1', 'A2'], 'bike':['A0'], 'truck': ['A1']}

def return_last(vehicle):
  return a[vehicle][-1]

return_last('car')

answered Jun 06 '18 at 07:22

Surya Tej

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Search a 2 dimensional python list for last occurrence in a particular column

3 Answers3

Use a dictionary