Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #71210 > unrolled thread

How to implement key of key in python?

Back to article view | Back to comp.lang.python

Contents

  How to implement key of key in python? eckhleung@gmail.com - 2014-05-09 18:22 -0700
    Re: How to implement key of key in python? CHIN Dihedral <dihedral88888@gmail.com> - 2014-05-09 19:21 -0700
    Re: How to implement key of key in python? MRAB <python@mrabarnett.plus.com> - 2014-05-10 03:30 +0100
      Re: How to implement key of key in python? eckhleung@gmail.com - 2014-05-09 20:28 -0700
        Re: How to implement key of key in python? Andrea D'Amore <anddamNOALPASTICCIODICARNE+gruppi@brapi.net> - 2014-05-10 09:07 +0200
        Re: How to implement key of key in python? Peter Otten <__peter__@web.de> - 2014-05-10 10:21 +0200

#71210 — How to implement key of key in python?

I'm migrating from Perl to Python and unable to identify the equivalent of key of key concept. The following codes run well,

import csv                                                                       
                                
attr = {}                                                                        
                                                                                 
with open('test.txt','rb') as tsvin:                                           
    tsvin = csv.reader(tsvin, delimiter='\t')                                    
                                                                                 
    for row in tsvin:                                                            
        ID = row[1]                                                             


until:
        attr[ID]['adm3'] = row[2]  

I then try:
        attr[ID].adm3 = row[2]

still doesn't work. Some posts suggest using module dict but some do not. I'm a bit confused now. Any suggestions?

[toc] | [next] | [standalone]

#71215

On Saturday, May 10, 2014 9:22:43 AM UTC+8, eckh...@gmail.com wrote:
> I'm migrating from Perl to Python and unable to identify the equivalent of key of key concept. The following codes run well,
> 
> 
> 
> import csv                                                                       
> 
>                                 
> 
> attr = {}                                                                        
> 
>                                                                                  
> 
> with open('test.txt','rb') as tsvin:                                           
> 
>     tsvin = csv.reader(tsvin, delimiter='\t')                                    
> 
>                                                                                  
> 
>     for row in tsvin:                                                            
> 
>         ID = row[1]                                                             
> 
> 
> 
> 
> 
> until:
> 
>         attr[ID]['adm3'] = row[2]  
> 
> 
> 
> I then try:
> 
>         attr[ID].adm3 = row[2]
> 
> 
> 
> still doesn't work. Some posts suggest using module dict but some do not. I'm a bit confused now. Any suggestions?

Please check your attr as an empty dictionary or so-called a hash in perl.

The syntax of adding a (K,V) pair 
is different between python and perl.

[toc] | [prev] | [next] | [standalone]

#71216

On 2014-05-10 02:22, eckhleung@gmail.com wrote:
> I'm migrating from Perl to Python and unable to identify the equivalent of key of key concept. The following codes run well,
>
> import csv
>
> attr = {}
>
> with open('test.txt','rb') as tsvin:
>      tsvin = csv.reader(tsvin, delimiter='\t')
>
>      for row in tsvin:
>          ID = row[1]
>
>
> until:
>          attr[ID]['adm3'] = row[2]
>
> I then try:
>          attr[ID].adm3 = row[2]
>
> still doesn't work. Some posts suggest using module dict but some do not. I'm a bit confused now. Any suggestions?
>
Python doesn't have Perl's autovivication feature. If you want the
value to be a dict then you need to create that dict first:

attr[ID] = {}
attr[ID]['adm3'] = row[2]

You could also have a look at the 'defaultdict' class in the
'collections' module.

[toc] | [prev] | [next] | [standalone]

#71220

On Saturday, May 10, 2014 10:30:06 AM UTC+8, MRAB wrote:
> On 2014-05-10 02:22, I wrote:
> 
> > I'm migrating from Perl to Python and unable to identify the equivalent of key of key concept. The following codes run well,
> 
> > import csv
> 
> > attr = {}
> 
> > with open('test.txt','rb') as tsvin:
> 
> >      tsvin = csv.reader(tsvin, delimiter='\t')
> 
> >      for row in tsvin:
> 
> >          ID = row[1]
> 
> > until:
> 
> >          attr[ID]['adm3'] = row[2]
> 
> > I then try:
> 
> >          attr[ID].adm3 = row[2]
> 
> > still doesn't work. Some posts suggest using module dict but some do not. I'm a bit confused now. Any suggestions?
> 
> Python doesn't have Perl's autovivication feature. If you want the
> 
> value to be a dict then you need to create that dict first:
> 
> attr[ID] = {}
> 
> attr[ID]['adm3'] = row[2]
>
> You could also have a look at the 'defaultdict' class in the
> 
> 'collections' module.

I identify the information below:
s = [('yellow', 1), ('blue', 2), ('yellow', 3), ('blue', 4), ('red', 1)]
d = defaultdict(list)
for k, v in s:
  d[k].append(v)

While it is fine for a small dataset, I need a more generic way to do so. Indeed the "test.txt" in my example contains more columns of attributes like:

ID address age gender phone-number race education ...
ABC123 Ohio, USA 18 F 800-123-456 european university
ACC499 London 33 M 800-111-400 african university
...

so later I can retrieve the information in python by:

attr['ABC123'].address (containing 'Ohio, USA')
attr['ABC123'].race (containing 'european')
attr['ACC499'].age (containing '33')

The following links mention something similar,

http://courses.cs.washington.edu/courses/cse140/13wi/csv-parsing.html
http://stackoverflow.com/questions/8800111/parse-csv-file-and-aggregate-the-values
http://stackoverflow.com/questions/17763642/reading-tab-separated-file-into-a-defaultdict-python
http://semanticbible.com/blogos/2009/06/12/reading-tab-delimited-data-in-python-with-csv/

unfortunately none of them illustrates how to store the values and access them later. Moreover, they bring some new terms, e.g. combined, [], etc.

Is there any better reference?

Thanks again!

[toc] | [prev] | [next] | [standalone]

#71225

On 2014-05-10 03:28:29 +0000, eckhleung@gmail.com said:

> While it is fine for a small dataset, I need a more generic way to do so.

I don't get how the dataset size affects the generality of the solution here.

From your first message:

> attr = {}
> with open('test.txt','rb') as tsvin:
>     tsvin = csv.reader(tsvin, delimiter='\t')
>     for row in tsvin:
>         ID = row[1]

so your is solved by adding a simple
  attr[ID] = {}

after the ID assignment. It seems simple to implement and generic enough to me.


> unfortunately none of them illustrates how to store the values and 
> access them later.

You access the stored value by using the variable name that holds it, 
but here you should probabily make more clear what your actual issue is.


> Moreover, they bring some new terms, e.g. combined, [], etc.

The "[]" syntax is used in Python for lists.

The term "combined" hasn't a specific pythonic meaning there and is 
just used as a meaningful variable name as the author is combining, 
i.e. adding, numerical values.


-- 
Andrea

[toc] | [prev] | [next] | [standalone]

#71237

eckhleung@gmail.com wrote:

> On Saturday, May 10, 2014 10:30:06 AM UTC+8, MRAB wrote:
>> On 2014-05-10 02:22, I wrote:
>> 
>> > I'm migrating from Perl to Python and unable to identify the equivalent
>> > of key of key concept. The following codes run well,
>> 
>> > import csv
>> 
>> > attr = {}
>> 
>> > with open('test.txt','rb') as tsvin:
>> 
>> >      tsvin = csv.reader(tsvin, delimiter='\t')
>> 
>> >      for row in tsvin:
>> 
>> >          ID = row[1]
>> 
>> > until:
>> 
>> >          attr[ID]['adm3'] = row[2]
>> 
>> > I then try:
>> 
>> >          attr[ID].adm3 = row[2]
>> 
>> > still doesn't work. Some posts suggest using module dict but some do
>> > not. I'm a bit confused now. Any suggestions?
>> 
>> Python doesn't have Perl's autovivication feature. If you want the
>> 
>> value to be a dict then you need to create that dict first:
>> 
>> attr[ID] = {}
>> 
>> attr[ID]['adm3'] = row[2]
>>
>> You could also have a look at the 'defaultdict' class in the
>> 
>> 'collections' module.
> 
> I identify the information below:
> s = [('yellow', 1), ('blue', 2), ('yellow', 3), ('blue', 4), ('red', 1)]
> d = defaultdict(list)
> for k, v in s:
>   d[k].append(v)
> 
> While it is fine for a small dataset, I need a more generic way to do so.
> Indeed the "test.txt" in my example contains more columns of attributes
> like:
> 
> ID address age gender phone-number race education ...
> ABC123 Ohio, USA 18 F 800-123-456 european university
> ACC499 London 33 M 800-111-400 african university
> ...
> 
> so later I can retrieve the information in python by:
> 
> attr['ABC123'].address (containing 'Ohio, USA')
> attr['ABC123'].race (containing 'european')
> attr['ACC499'].age (containing '33')

Using a csv.DictReader comes close with minimal effort:

# write demo data to make the example self-contained
with open("tmp.csv", "w") as f:
    f.write("""\
ID,address,age,gender,phone-number,race,education
ABC123,"Ohio, USA",18,F,800-123-456,european,university
ACC499,London,33,M,800-111-400,african,university
""")

import csv
import pprint

with open("tmp.csv") as f:
    attr = {row["ID"]: row for row in csv.DictReader(f)}
        
pprint.pprint(attr)

print(attr["ACC499"]["age"])

The "dict comprehension"

    attr = {row["ID"]: row for row in csv.DictReader(f)}

is a shortcut for

attr = {}
for row in csv.DictReader(f):
    attr[row["ID"]] = row

If you insist on attribute access (row.age instead of row["age"]) you can 
use a namedtuple. This is a bit more involved:

import csv
import pprint
from collections import namedtuple

with open("tmp.csv") as f:
    rows = csv.reader(f)
    header = next(rows)

    # make sure column names are valid Python identifiers
    header = [column.replace("-", "_") for column in header]

    RowType = namedtuple("RowType", header)
    key_index = header.index("ID")
    attr = {row[key_index]: RowType(*row) for row in rows}

pprint.pprint(attr)

print(attr["ABC123"].race)

> The following links mention something similar,

Too many, so I checked none of them ;)

[toc] | [prev] | [standalone]

Back to top | Article view | comp.lang.python

csiph-web