Get the length of certain values from list

Question

I would like to get the length of certain values in a list like:

lst=['ID_CYTY', 'CITY', 'ID_STATE', 'STATE', 'ID_COUNTRY', 'COUNTRY', 'AGE', 'SEX', 'NAME', 'P', 'A1', 'PR', 'V', 'Z', 'M1', 'D1', 'R1', 'CPD', 'CA', 'IN', 'ND', 'I', 'C', 'W', 'NZ', 'EG', 'LOS', 'TO', 'LS', 'EST', 'TR', 'OBS', 'RUT']

I just have another list like:

lst2=['P', 'A1', 'PR', 'V', 'Z', 'M1', 'D1', 'R1', 'CPD', 'CA', 'IN', 'ND', 'I', 'C', 'W']

I would like to get the length of the values before and after lst2 that are inside lst but the issue here is that lst could change in length from ID_CITY to NAME and NZ to RUT, I mean it could have more or less strings after P to W. Also, do not have to use the names of the strings because they could be different from the 0 index to the last index, example:

lst=['CITY', 'ID_STATE', 'STATE', 'ID_COUNTRY', 'COUNTRY', 'AGE', 'SEX', 'A1', 'P', 'PR', 'V', 'Z', 'M1', 'D1', 'R1', 'CPD', 'CA', 'W', 'ND', 'I', 'C', 'IN', 'NZ', 'LOS', 'TO', 'LS', 'EST', 'TR', 'OBS']

I believe it could be done getting the length of the lst2 and then doing some list indexing to get lengths inside lst.

The lst2 it could have theirs strings mixed but it doesn't matter because it must have the same extension from P to W no matter if starts or ends with those strings.

Note: I would like to get the values before and after lst2 in lst in individual list.

What I mean with before and after lst2 inside lst is: In the first case it would be: The length before P to W:

the length from NZ to RUT:

But this could be different just how I mentioned before.

```python lst2 = list(filter(lambda n: len(name) <= 3, lst)) ``` — Ozballer31, Nov 11 '20 at 20:12
What do you mean by before and after `lst2`. Please add the input and the corresponding output? Also include any code you have written — Dani Mesejo, Nov 11 '20 at 20:20
your question is very unclear what do you actually want in the end? — coderoftheday, Nov 11 '20 at 20:34
@DaniMesejo It looks like `lst2` is a sublist of `lst`, so he wants the parts of `lst` outside that sublist. — Barmar, Nov 11 '20 at 20:35
but, what's the thing with the new items in the list, that still confuses me. @Barmar — coderoftheday, Nov 11 '20 at 20:39
@Barmar Yes. Thanks for all your comments. What I want are the lengths before an after `['P':'W']` in individual variables. Hope to be clearer. — MetalJacket, Nov 11 '20 at 20:39
@coderoftheday What do you mean by new items? I think he's just saying that the lists can vary, you shouldn't look for those specific strings. — Barmar, Nov 11 '20 at 20:43
@DaniMesejo `P` is the first element of `lst2`, `W` is the last. — Barmar, Nov 11 '20 at 20:43
Not yet, because I do not need to specify any name index and specify index position because they could be mixed @coderoftheday — MetalJacket, Nov 11 '20 at 21:06
What I was thinking is first get the `len(lst2)` and then do some string indexing to get the first and last values in differents variables. The `len` of `lst2` always would be a section or slide of lst. — MetalJacket, Nov 11 '20 at 21:12

Barmar · Accepted Answer · 2020-11-11T21:17:49.963

1

See Python: return the index of the first element of a list which makes a passed function true for how to find the index in a list of the first element that matches a condition.

In this case, the length of the list before lst2 is the index of the first element that's in lst2.

before = next(i for i,v in enumerate(lst) if v in lst2)

To get the length of the list after lst2, do the same thing but reverse lst first.

after = next(i for i,v in enumerate(lst[::-1]) if v in lst2)

edited Nov 11 '20 at 21:17

answered Nov 11 '20 at 20:49

Barmar

741,623
53
500
612

Thanks. It works but there is an issue when index are mixed. I mean, when `lst2` have 'A1', 'P', it counts more if all is mixed. That's the other possibility that could happen here. The length of lst2 always will be inside lst but the index it could be mixed @Barmar – MetalJacket Nov 11 '20 at 20:59
I thought the order of elements in `lst2` are the same as in `lst`, so it's always the first and last that it has to look for. – Barmar Nov 11 '20 at 20:59
Any other idea? @Barmar – MetalJacket Nov 11 '20 at 21:13
Hi @Barmar. I'm facing new issues when `lst` have `'A1, 'Ps, 'PRz'` it gives me a different length in `before`. – MetalJacket Nov 20 '20 at 19:37

score 1 · Answer 2 · answered Nov 11 '20 at 21:54

#lst=['ID_CYTY', 'CITY', 'ID_STATE', 'STATE', 'ID_COUNTRY', 'COUNTRY', 'AGE', 'SEX', 'NAME', 'P', 'A1', 'PR', 'V', 'Z', 'M1', 'D1', 'R1', 'CPD', 'CA', 'IN', 'ND', 'I', 'C', 'W', 'NZ', 'EG', 'LOS', 'TO', 'LS', 'EST', 'TR', 'OBS', 'RUT']
lst=['CITY', 'ID_STATE', 'STATE', 'ID_COUNTRY', 'COUNTRY', 'AGE', 'SEX', 'A1', 'P', 'PR', 'V', 'Z', 'M1', 'D1', 'R1', 'CPD', 'CA', 'W', 'ND', 'I', 'C', 'IN', 'NZ', 'LOS', 'TO', 'LS', 'EST', 'TR', 'OBS']
lst2=['P', 'A1', 'PR', 'V', 'Z', 'M1', 'D1', 'R1', 'CPD', 'CA', 'IN', 'ND', 'I', 'C', 'W']

for i in lst:
    if i in lst2:
        start = lst.index(i)
        break
for i in lst[::-1]:
    if i in lst2:
        end = lst.index(i)
        break

print(len(lst[:start]))
print(len(lst[end:-1]))

Now even if both lists changed it finds the first and last value to calculate from

Alexander · Answer 3 · 2020-11-11T20:43:13.937

0

You could use

start = lst.index(lst2[0])

This will give you the position, in lst, of the first value in lst2

end = lst.index(lst2[-1])

This will give you the position, in lst, of the last value in lst2

print(len(lst[0:start]))
print(len(lst[end:-1]))

This prints the lengths between the values

edited Nov 11 '20 at 20:43

answered Nov 11 '20 at 20:34

Alexander

11
2

He just wants the lengths, so they're `start` and `len(lst) - end` – Barmar Nov 11 '20 at 20:40
Yes. How can I get it using `lst2`? @Barmar – MetalJacket Nov 11 '20 at 20:41
`[end:-1]` should be `[end+1:]` – Barmar Nov 11 '20 at 20:45
@Barmar It works with start but not using this `lst.index(lst2[-1])` the output is 23 – MetalJacket Nov 11 '20 at 20:45
@MetalJacket That's why you have to subtract: `len(lst) - lst.index(lst2[-1])` – Barmar Nov 11 '20 at 20:46
@Barmar yes 23 is the position in lst. I use that to show where the start of the values are – Alexander Nov 11 '20 at 20:50
The code outputs 9 and 9 which is what he wanted in his example – Alexander Nov 11 '20 at 20:51

coderoftheday · Answer 4 · 2020-11-11T21:18:56.280

0

This does what comment 'What I was thinking is first get the len(lst2) and then do some string indexing to get the first and last values in differents variables. The len of lst2 always would be a section or slide of lst. –' says.

lst=['ID_CYTY', 'CITY', 'ID_STATE', 'STATE', 'ID_COUNTRY', 'COUNTRY', 'AGE', 'SEX', 'NAME', 'P', 'A1', 'PR', 'V', 'Z', 'M1', 'D1', 'R1', 'CPD', 'CA', 'IN', 'ND', 'I', 'C', 'W', 'NZ', 'EG', 'LOS', 'TO', 'LS', 'EST', 'TR', 'OBS', 'RUT']
lst2=['P', 'A1', 'PR', 'V', 'Z', 'M1', 'D1', 'R1', 'CPD', 'CA', 'IN', 'ND', 'I', 'C', 'W']

legnth_1= len(lst[:lst.index(lst2[0])])
legnth_2 =  len(lst[lst.index(lst2[-1])+1:])

print(legnth_1)
print(legnth_2)


>>> 9
>>> 9

edited Nov 11 '20 at 21:18

answered Nov 11 '20 at 20:43

coderoftheday

1,987
4
7
21

1

I don't think he wants the combined lengths, he wants the lengths of the parts before and after `lst2` separately. – Barmar Nov 11 '20 at 20:47
Yes, and also I do not need to specify any name index because it could be mixed. – MetalJacket Nov 11 '20 at 21:04
So how we meant to know where the index will be? what are we using to determine the index – coderoftheday Nov 11 '20 at 21:05
Thanks for the updated. Finally, I think its working fine. I would try some other times but it seems work very well @coderoftheday – MetalJacket Nov 11 '20 at 21:26

score 0 · Answer 5 · answered Nov 11 '20 at 21:25

lst=['ID_CYTY', 'CITY', 'ID_STATE', 'STATE', 'ID_COUNTRY', 'COUNTRY', 'AGE', 'SEX', 'NAME', 'P', 'A1', 'PR', 'V', 'Z', 'M1', 'D1', 'R1', 'CPD', 'CA', 'IN', 'ND', 'I', 'C', 'W', 'NZ', 'EG', 'LOS', 'TO', 'LS', 'EST', 'TR', 'OBS', 'RUT']
lst2=['P', 'A1', 'PR', 'V', 'Z', 'M1', 'D1', 'R1', 'CPD', 'CA', 'IN', 'ND', 'I', 'C', 'W']

start = lst.index(lst2[0])
end = lst.index(lst2[-1])

print(len(lst[:start]))
print(len(lst[end:-1]))

>>>
9
9
>>>

Even if the list changes it still returns the difference

lst=['CITY', 'ID_STATE', 'STATE', 'ID_COUNTRY', 'COUNTRY', 'AGE', 'SEX', 'A1', 'P', 'PR', 'V', 'Z', 'M1', 'D1', 'R1', 'CPD', 'CA', 'W', 'ND', 'I', 'C', 'IN', 'NZ', 'LOS', 'TO', 'LS', 'EST', 'TR', 'OBS']

>>>
8
11
>>>

But what if `lst2` changes or their values get mixed?. I mean if not starts with `P` or ends with another string. @Alexander — MetalJacket, Nov 11 '20 at 21:35

Get the length of certain values from list

5 Answers5