Count the number of elements in a string separated by comma

Question

I am dealing with text strings such as the following: LN1 2DW, DN21 5BJ, DN21 5BL, ...

In Python, how can I count the number of elements between commas? Each element can be made of 6, 7, or 8 characters, and in my example there are 3 elements shown. The separator is always a comma.

I have never done anything related to text mining so this would be a start for me.

score 29 · Accepted Answer · edited Jan 10 '17 at 14:54

29

You can count the number of commas:

text.count(",") + 1
# 3

edited Jan 10 '17 at 14:54

Willem Van Onsem

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answered Jan 10 '17 at 14:53

Psidom

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I'm curious to see a benchmark of this approach (str.count()) vs. split + len. If you have the time, feel free. :-) – Bram Vanroy Jun 20 '18 at 12:03
Yes I'd also like to know what's more efficient - counting commas or splitting and using len? – KMunro Nov 12 '19 at 15:19
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@BramVanroy Done a real quick test using `ipython` and its `%timeit` built-in. Results: `text.count(',')+1`: 665 ns ± 3.06 ns per loop `len(text.split(','))`: 3.59 µs ± 19.3 ns per loop Tested data was a list of 91 elements. – Skillmon Jan 23 '20 at 13:42
@KMunro see my earlier comment. – Skillmon Jan 23 '20 at 13:43

Willem Van Onsem · Answer 2 · 2017-01-10T14:53:34.760

13

If the comma (,) is the separator, you can simply use str.split on the string and then len(..) on the result:

text = 'LN1 2DW, DN21 5BJ, DN21 5B'
number = len(text.split(','))

You can also reuse the list of elements. For instance:

text = 'LN1 2DW, DN21 5BJ, DN21 5B'
tags = text.split(',')
number = len(tags)
#do something with the `tags`

edited Jan 10 '17 at 14:53

answered Jan 10 '17 at 14:50

Willem Van Onsem

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Text.count (',')+1 – Joran Beasley Jan 10 '17 at 14:52
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This work indeed more efficiently, but the next step is probably iterating over the elements. – Willem Van Onsem Jan 10 '17 at 14:52
Spaces are not ignored here – sagar Jan 10 '17 at 15:26
@sagar: in the loop, one can use `.strip` etc. to simply post-process every element. – Willem Van Onsem Jan 10 '17 at 15:28
I'm curious to see a benchmark of this approach (split + len) vs. str.count(). If you have the time, feel free. :-) – Bram Vanroy Jun 20 '18 at 12:03
@BramVanroy: well `.split(..)` is definitely less efficient. It first of all will result in a linear amount of `malloc`s, and furthermore most Python interpreters use some flyweight patterns. – Willem Van Onsem Jun 20 '18 at 12:05

Uri Goren · Answer 3 · 2017-01-10T15:03:43.353

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Willien and Psidom already mentioned count,

I just wanted to add that in python a string is also iteratable, thus list comprehension could also be applied:

n = len([c for c in ','+text if c==','])

Or

n = sum(1 for c in ','+text if c==',')

edited Jan 10 '17 at 15:03

answered Jan 10 '17 at 14:59

Uri Goren

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Why would you do this? SO should provide the best answers not all possible alternatives – Chris_Rands Jan 10 '17 at 15:00
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Feel free to vote down, if my answer is against SO policy I'm sure you could ask a moderator to delete it – Uri Goren Jan 10 '17 at 15:35
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You're not breaking any rules, but why present worse alternatives than existing answers. There are so many possible answers, like you could include `len(list(filter(lambda x: ord(x) == 44, text)))+1` too but it really doesn't add anything – Chris_Rands Jan 10 '17 at 15:49

Count the number of elements in a string separated by comma

3 Answers3