Continuing playing with Reddit data, I thought that it might be fun to extract discussed topics from subreddits. My idea was: get comments from a subreddit, extract ngrams, calculate counts of ngrams, normalize counts, and subtract them from normalized counts of ngrams from a neutral set of comments.

### Small-scale

For proving the idea on a smaller scale, I’ve fetched titles, texts and the first three levels of comments from top 1000 r/all posts (full code available in a gist), as it should have a lot of texts from different subreddits:

``````get_subreddit_df('all').head()
``````
id subreddit post_id kind text created score
0 7mjw12_title all 7mjw12 title My cab driver tonight was so excited to share ... 1.514459e+09 307861
1 7mjw12_selftext all 7mjw12 selftext 1.514459e+09 307861
2 7mjw12_comment_druihai all 7mjw12 comment I want to make good humored inappropriate joke... 1.514460e+09 18336
3 7mjw12_comment_drulrp0 all 7mjw12 comment Me too! It came out of nowhere- he was pretty ... 1.514464e+09 8853
4 7mjw12_comment_druluji all 7mjw12 comment Well, you got him to the top of Reddit, litera... 1.514464e+09 4749

Lemmatized texts, get all 1-3 words ngrams and counted them:

``````df = get_tokens_df(subreddit)  # Full code is in gist
df.head()
``````
token amount
0 cab 84
1 driver 1165
2 tonight 360
3 excited 245
4 share 1793

Then I’ve normalized counts:

``````df['amount_norm'] = (df.amount - df.amount.mean()) / (df.amount.max() - df.amount.min())
df.head()
``````
token amount amount_norm
0 automate 493 0.043316
1 boring 108 0.009353
2 stuff 1158 0.101979
3 python 11177 0.985800
4 tinder 29 0.002384

And as the last step, I’ve calculated diff and got top 5 ngrams with texts from top 1000 posts from some random subreddits. Seems to be working for r/linux:

``````diff_tokens(tokens_dfs['linux'], tokens_dfs['all']).head()
``````
token amount_diff amount_norm_diff
5807 kde 3060.0 1.082134
2543 debian 1820.0 1.048817
48794 coc 1058.0 1.028343
9962 systemd 925.0 1.024769
11588 gentoo 878.0 1.023506

Also looks ok on r/personalfinance:

``````diff_tokens(tokens_dfs['personalfinance'], tokens_dfs['all']).head()
``````
token amount_diff amount_norm_diff
78063 vanguard 1513.0 1.017727
18396 etf 1035.0 1.012113
119206 checking account 732.0 1.008555
60873 direct deposit 690.0 1.008061
200917 joint account 679.0 1.007932

And kind of funny with r/drunk:

``````diff_tokens(tokens_dfs['drunk'], tokens_dfs['all']).head()
``````
token amount_diff amount_norm_diff
515158 honk honk honk 144.0 1.019149
41088 pbr 130.0 1.017247
49701 mo dog 129.0 1.017112
93763 cheap beer 74.0 1.009641
124756 birthday dude 61.0 1.007875

Seems to be working on this scale.

### A bit larger scale

As the next iteration, I’ve decided to try the idea on three months of comments, which I was able to download as dumps from pushift.io.

#### Shaping the data

And it’s kind of a lot of data, even compressed:

``````\$ du -sh raw_data/*
11G	raw_data/RC_2018-08.xz
10G	raw_data/RC_2018-09.xz
11G	raw_data/RC_2018-10.xz
``````

Pandas basically doesn’t work on that scale, and unfortunately, I don’t have a personal Hadoop cluster. So I’ve reinvented a wheel a bit:

graph LR A[Reddit comments]-->B[Reddit comments wiht ngrams] B-->C[Ngrams partitioned by subreddit and day] C-->D[Counted partitioned ngrams]

The raw data is stored in line-delimited JSON, like:

``````\$ xzcat raw_data/RC_2018-10.xz | head -n 2
{"archived":false,"author":"TistedLogic","author_created_utc":1312615878,"author_flair_background_color":null,"author_flair_css_class":null,"author_flair_richtext":[],"author_flair_template_id":null,"author_flair_text":null,"author_flair_text_color":null,"author_flair_type":"text","author_fullname":"t2_5mk6v","author_patreon_flair":false,"body":"Is it still r\/BoneAppleTea worthy if it's the opposite?","can_gild":true,"can_mod_post":false,"collapsed":false,"collapsed_reason":null,"controversiality":0,"created_utc":1538352000,"distinguished":null,"edited":false,"gilded":0,"gildings":{"gid_1":0,"gid_2":0,"gid_3":0},"id":"e6xucdd","is_submitter":false,"link_id":"t3_9ka1hp","no_follow":true,"parent_id":"t1_e6xu13x","permalink":"\/r\/Unexpected\/comments\/9ka1hp\/jesus_fking_woah\/e6xucdd\/","removal_reason":null,"retrieved_on":1539714091,"score":2,"send_replies":true,"stickied":false,"subreddit":"Unexpected","subreddit_id":"t5_2w67q","subreddit_name_prefixed":"r\/Unexpected","subreddit_type":"public"}
{"archived":false,"author":"misssaladfingers","author_created_utc":1536864574,"author_flair_background_color":null,"author_flair_css_class":null,"author_flair_richtext":[],"author_flair_template_id":null,"author_flair_text":null,"author_flair_text_color":null,"author_flair_type":"text","author_fullname":"t2_27d914lh","author_patreon_flair":false,"body":"I've tried and it's hit and miss. When it's good I feel more rested even though I've not slept well but sometimes it doesn't work","can_gild":true,"can_mod_post":false,"collapsed":false,"collapsed_reason":null,"controversiality":0,"created_utc":1538352000,"distinguished":null,"edited":false,"gilded":0,"gildings":{"gid_1":0,"gid_2":0,"gid_3":0},"id":"e6xucde","is_submitter":false,"link_id":"t3_9k8bp4","no_follow":true,"parent_id":"t1_e6xu9sk","permalink":"\/r\/insomnia\/comments\/9k8bp4\/melatonin\/e6xucde\/","removal_reason":null,"retrieved_on":1539714091,"score":1,"send_replies":true,"stickied":false,"subreddit":"insomnia","subreddit_id":"t5_2qh3g","subreddit_name_prefixed":"r\/insomnia","subreddit_type":"public"}
``````

The first script `add_ngrams.py` reads lines of raw data from stdin, adds 1-3 lemmatized ngrams and writes lines in JSON to stdout. As the amount of data is huge, I’ve gzipped the output. It took around an hour to process month worth of comments on 12 CPU machine. Spawning more processes didn’t help as thw whole thing is quite CPU intense.

``````\$ xzcat raw_data/RC_2018-10.xz | python3.7 add_ngrams.py | gzip > with_ngrams/2018-10.gz
\$ zcat with_ngrams/2018-10.gz | head -n 2
{"archived": false, "author": "TistedLogic", "author_created_utc": 1312615878, "author_flair_background_color": null, "author_flair_css_class": null, "author_flair_richtext": [], "author_flair_template_id": null, "author_flair_text": null, "author_flair_text_color": null, "author_flair_type": "text", "author_fullname": "t2_5mk6v", "author_patreon_flair": false, "body": "Is it still r/BoneAppleTea worthy if it's the opposite?", "can_gild": true, "can_mod_post": false, "collapsed": false, "collapsed_reason": null, "controversiality": 0, "created_utc": 1538352000, "distinguished": null, "edited": false, "gilded": 0, "gildings": {"gid_1": 0, "gid_2": 0, "gid_3": 0}, "id": "e6xucdd", "is_submitter": false, "link_id": "t3_9ka1hp", "no_follow": true, "parent_id": "t1_e6xu13x", "permalink": "/r/Unexpected/comments/9ka1hp/jesus_fking_woah/e6xucdd/", "removal_reason": null, "retrieved_on": 1539714091, "score": 2, "send_replies": true, "stickied": false, "subreddit": "Unexpected", "subreddit_id": "t5_2w67q", "subreddit_name_prefixed": "r/Unexpected", "subreddit_type": "public", "ngrams": ["still", "r/boneappletea", "worthy", "'s", "opposite", "still r/boneappletea", "r/boneappletea worthy", "worthy 's", "'s opposite", "still r/boneappletea worthy", "r/boneappletea worthy 's", "worthy 's opposite"]}
{"archived": false, "author": "1-2-3RightMeow", "author_created_utc": 1515801270, "author_flair_background_color": null, "author_flair_css_class": null, "author_flair_richtext": [], "author_flair_template_id": null, "author_flair_text": null, "author_flair_text_color": null, "author_flair_type": "text", "author_fullname": "t2_rrwodxc", "author_patreon_flair": false, "body": "Nice! I\u2019m going out for dinner with him right and I\u2019ll check when I get home. I\u2019m very interested to read that", "can_gild": true, "can_mod_post": false, "collapsed": false, "collapsed_reason": null, "controversiality": 0, "created_utc": 1538352000, "distinguished": null, "edited": false, "gilded": 0, "gildings": {"gid_1": 0, "gid_2": 0, "gid_3": 0}, "id": "e6xucdp", "is_submitter": true, "link_id": "t3_9k9x6m", "no_follow": false, "parent_id": "t1_e6xsm3n", "permalink": "/r/Glitch_in_the_Matrix/comments/9k9x6m/my_boyfriend_and_i_lost_10_hours/e6xucdp/", "removal_reason": null, "retrieved_on": 1539714092, "score": 42, "send_replies": true, "stickied": false, "subreddit": "Glitch_in_the_Matrix", "subreddit_id": "t5_2tcwa", "subreddit_name_prefixed": "r/Glitch_in_the_Matrix", "subreddit_type": "public", "ngrams": ["nice", "go", "dinner", "right", "check", "get", "home", "interested", "read", "nice go", "go dinner", "dinner right", "right check", "check get", "get home", "home interested", "interested read", "nice go dinner", "go dinner right", "dinner right check", "right check get", "check get home", "get home interested", "home interested read"]}
``````

The next script `partition.py` reads stdin and writes files like `2018-10-10_AskReddit` with just ngrams to a folder passed as an argument.

``````\$ zcat with_ngrams/2018-10.gz | python3.7 parition.py partitions
\$ cat partitions/2018-10-10_AskReddit | head -n 5
"gt"
"money"
"go"
"administration"
"building"
``````

For three months of comments it created a lot of files:

``````\$ ls partitions | wc -l
2715472
``````

After that I’ve counted ngrams in partitions with `group_count.py`:

``````\$ python3.7 group_count.py partitions counted
\$ cat counted/2018-10-10_AskReddit | head -n 5
["gt", 7010]
["money", 3648]
["go", 25812]
["administration", 108]
["building", 573]
``````

As r/all isn’t a real subreddit and it’s not possible to get it from the dump, I’ve chosen r/AskReddit as a source of “neutral” ngrams, for that I’ve calculated the aggregated count of ngrams with `aggreage_whole.py`:

``````\$ python3.7 aggreage_whole.py AskReddit > aggregated/askreddit_whole.json
\$ cat aggregated/askreddit_whole.json | head -n 5
[["trick", 26691], ["people", 1638951], ["take", 844834], ["zammy", 10], ["wine", 17315], ["trick people", 515], ["people take", 10336], ["take zammy", 2], ["zammy wine", 2], ["trick people take", 4], ["people take zammy", 2]...
``````

#### Playing with the data

First of all, I’ve read “neutral” ngrams, removed ngrams appeared less than 100 times as otherwise it wasn’t fitting in RAM and calculated normalized count:

``````whole_askreddit_df = pd.read_json('aggregated/askreddit_whole.json', orient='values')
whole_askreddit_df = whole_askreddit_df.rename(columns={0: 'ngram', 1: 'amount'})
whole_askreddit_df = whole_askreddit_df[whole_askreddit_df.amount > 99]
whole_askreddit_df['amount_norm'] = norm(whole_askreddit_df.amount)
``````
ngram amount amount_norm
0 trick 26691 0.008026
1 people 1638951 0.492943
2 take 844834 0.254098
4 wine 17315 0.005206
5 trick people 515 0.000153

To be sure that the idea is still valid, I’ve randomly checked r/television for 10th October:

``````television_10_10_df = pd \
.read_json('counted/2018-10-10_television', lines=True) \
.rename(columns={0: 'ngram', 1: 'amount'})
television_10_10_df['amount_norm'] = norm(television_10_10_df.amount)
television_10_10_df = television_10_10_df.merge(whole_askreddit_df, how='left', on='ngram', suffixes=('_left', '_right'))
television_10_10_df['diff'] = television_10_10_df.amount_norm_left - television_10_10_df.amount_norm_right
television_10_10_df \
.sort_values('diff', ascending=False) \
.head()
``````
ngram amount_left amount_norm_left amount_right amount_norm_right diff
13 show 1299 0.699950 319715.0 0.096158 0.603792
32 season 963 0.518525 65229.0 0.019617 0.498908
19 character 514 0.276084 101931.0 0.030656 0.245428
4 episode 408 0.218849 81729.0 0.024580 0.194269
35 watch 534 0.286883 320204.0 0.096306 0.190578

And just for fun, limiting to trigrams:

``````television_10_10_df\
[television_10_10_df.ngram.str.count(' ') >= 2] \
.sort_values('diff', ascending=False) \
.head()
``````
ngram amount_left amount_norm_left amount_right amount_norm_right diff
11615 better call saul 15 0.006646 1033.0 0.000309 0.006337
36287 would make sense 11 0.004486 2098.0 0.000629 0.003857
7242 ca n't wait 12 0.005026 5396.0 0.001621 0.003405
86021 innocent proven guilty 9 0.003406 1106.0 0.000331 0.003075
151 watch first episode 8 0.002866 463.0 0.000137 0.002728

Seems to be ok, as the next step I’ve decided to get top 50 discussed topics for every available day:

``````r_television_by_day = diff_n_by_day(  # in the gist
50, whole_askreddit_df, 'television', '2018-08-01', '2018-10-31',
exclude=['r/television'],
)
r_television_by_day[r_television_by_day.date == "2018-10-05"].head()
``````
ngram amount_left amount_norm_left amount_right amount_norm_right diff date
3 show 906 0.725002 319715.0 0.096158 0.628844 2018-10-05
8 season 549 0.438485 65229.0 0.019617 0.418868 2018-10-05
249 character 334 0.265933 101931.0 0.030656 0.235277 2018-10-05
1635 episode 322 0.256302 81729.0 0.024580 0.231723 2018-10-05
418 watch 402 0.320508 320204.0 0.096306 0.224202 2018-10-05

Then I thought that it might be fun to get overall top topics from daily top topics and make a weekly heatmap with seaborn:

``````r_television_by_day_top_topics = r_television_by_day \
.groupby('ngram') \
.sum()['diff'] \
.reset_index() \
.sort_values('diff', ascending=False)

r_television_by_day_top_topics.head()
``````
ngram diff
916 show 57.649622
887 season 37.241199
352 episode 22.752369
1077 watch 21.202295
207 character 15.599798
``````r_television_only_top_df = r_television_by_day \
[['date', 'ngram', 'diff']] \
[r_television_by_day.ngram.isin(r_television_by_day_top_topics.ngram.head(10))] \
.groupby([pd.Grouper(key='date', freq='W-MON'), 'ngram']) \
.mean() \
.reset_index() \
.sort_values('date')

pivot = r_television_only_top_df \
.pivot(index='ngram', columns='date', values='diff') \
.fillna(-1)

sns.heatmap(pivot, xticklabels=r_television_only_top_df.date.dt.week.unique())
``````

And it was quite boring, I’ve decided to try weekday heatmap, but it wasn’t better as topics were the same:

``````weekday_heatmap(r_television_by_day, 'r/television weekday')  # in the gist
``````

Heatmaps for r/programming are also boring:

``````r_programming_by_day = diff_n_by_day(  # in the gist
50, whole_askreddit_df, 'programming', '2018-08-01', '2018-10-31',
exclude=['gt', 'use', 'write'],  # selected manully
)
weekly_heatmap(r_programming_by_day, 'r/programming')
``````

Although a heatmap by a weekday is a bit different:

``````weekday_heatmap(r_programming_by_day, 'r/programming by weekday')
``````

Another popular subreddit – r/sports:

``````r_sports_by_day = diff_n_by_day(
50, whole_askreddit_df, 'sports', '2018-08-01', '2018-10-31',
exclude=['r/sports'],
)
weekly_heatmap(r_sports_by_day, 'r/sports')
``````

``````weekday_heatmap(r_sports_by_day, 'r/sports by weekday')
``````

As the last subreddit for giggles – r/drunk:

``````r_drunk_by_day = diff_n_by_day(50, whole_askreddit_df, 'drunk', '2018-08-01', '2018-10-31')
weekly_heatmap(r_drunk_by_day, 'r/drunk')
``````

``````weekday_heatmap(r_drunk_by_day, "r/drunk by weekday")
``````

### Conclusion

The idea kind of works for generic topics of subreddits, but can’t be used for finding trends.

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