If you've ever tried to do anything with data provided to you in PDFs, you know how painful it is — it's hard to copy-and-paste rows of data out of PDF files. It's especially hard if you want to retain the formats of the data in PDF file while extracting text. Most of the open source PDF parsers available are good at extracting text. But when it comes to retaining the the file's structure, eh, not really. Try tabula-py to extract data into a CSV or Excel spreadsheet using a simple, easy-to-use interface. One look is worth a thousand words. Take a look at the demo screenshot.
Installations¶
Readdle is a pioneer of iOS App Store, one of the first companies to create file management and scanning apps on the App Store. Our main goal is to help you, boost your productivity and give you the ability to use tools that haven't been available on mobile devices before. Scan documents, sign contracts, plan your day, print from any iOS device - that's what our apps allow you to do. Hashes for lightnovelcrawler-2.23.2-py3-none-any.whl; Algorithm Hash digest; SHA256: 347da8f71406d5f6b66012855620d365b1b7a253a08a.
- ACAD DWG to PDF Converter 9.8.2.6. SmartDWG DWG to PDF Converter 2.13. Convert DWG, DWF, and DXF files to PDF by resorting to this approachable piece of software that do.
- Are used to convert your USGA Handicap Index to a Course Handicap for the course and tees you are playing. 11.1 to 13.1 6 13.2 to 15.1 7 15.2 to 17.1 8 17.2 to 19.1 9 19.2 to 21.1 10 21.2 to 23.2 11 23.3 to 25.2 12 25.3 to 27.2 13 27.3 to 29.2 14 29.3 to 31.2 15 31.3 to 33.2 16.
This installation tutorial assumes that you are using Windows. However, according to the offical tabula-py documentation, it was confirmed that tabula-py works on macOS and Ubuntu.
1. Download Java
Tabula-py is a wrapper for tabula-java, which translates Python commands to Java commands. As the name 'tabula-java' suggests, it requires Java. You can download Java here.
2. Set environment PATH variable (Windows)
One thing that I don't like about Windows is that it's difficult to use a new program I downloaded in a console environment like Python or CMD window. But oh well, if you are a Windows user, you have to go through this extra step to allow Python to use Java. If you are a macOS or Ubuntu user, you probably don't need this step.
Find where Java is installed, and go to Control Panel > System and Security > System > Advanced system settings > Advanced > Environment Variables.
to set environment PATH variable for Java.
Make sure you have Javajdk1.8.0_201bin
and Javajre1.8.0_201bin
in the environment path variable. Then, type java -version
on CMD window. If you successfully installed Java and configured the environment variable, you should see something like this:
If you don't see something like this, it means that you didn't properly configure environment PATH variable for Java.
3. Re-start Your Command Prompt
Any program invoked from the command prompt will be given the environment variables that was at the time the command prompt was invoked. If you launched your Python console or Jupyter Notebook before you updated your environment PATH variable, you need to re-start again. Otherwise the change in the environment variable will not be reflected.
If you are experiencing FileNotFoundError
or 'java' is not recognized as an internal or external command, operable program or batch file
inside Jupyter or Python console, it's the issue of environment variable. Either you set it wrong, or your command prompt is not reflecting the change you made in the environment variable.
http://gahdes.xtgem.com/Blog/__xtblog_entry/19307362-pokemon-roms-for-windows-phone#xt_blog. To check if the change in the environment variable was reflected, run the following code in Jupyter or Python console:
Something like these must be in the output if everything is working fine:
4. Install Tabula-py
This is the last step:
Make sure that you install tabula-py
, not tabula
. Failing to do so will result in AttributeError: module 'tabula' has no attribute 'read_pdf', as discussed in this thread. Omnifocus pro 2 4 download free. More detailed instructions are provided in the github repo of tabula-py
Tabula Web Application¶
Tabula supports web application to parse PDF files. You do not need this to use tabula-py, but from my personal experience I strongly recommend you to use this tool because it really helps you debugging issues when using tabula-py. For example, I was tring to parse 100s of PDF files at once, and for some reason tabula-py would return an NoneType
object instead of pd.DataFrame
object (by default, tabula-py extracts tables in dataframe) for one PDF file. There was nothing wrong with my codes, and yet it would just not parse the file. So I tried opening it on the tabula web-app, and realized that it was actually a scanned PDF file and that tabula is unable to parse scanned PDFs.
Long story short, if it can be parsed with tabula web-app, you can replicate it with tabula-py. If tabula web-app can't, you should probably look for a different tool.
Installations
If you already configured the environment PATH variable for Java, all you need to do is downloading the .zip file here and running tabula.exe
. That's it. Tabula has really nice web UI that allows you to parse tables from PDFs by just clicking buttons.
Note
The web-app will automatically open in your browser with 127.0.0.1:8080 local host. If port 8080 is already being used by another process, you will need to shut it down. Spotfiles 3 0 16 – find files without spotlight. But normally you don't have to worry about this.
Screenshots
This is what you will see when you launch tabula.exe
. Browse.
the PDF file you want to parse, and import
.
You can either use Autodetect Tables
or drag your mouse to choose the area of your interest. If the PDF file has a complicated structure, it is usually better to manually choose the area of your interest. Also, note the option Repeat to All Pages
. Selecting this option will apply the area you chose for all pages.
Here's the output. More explanation about Lattice
and Stream
options will be discussed in detail later.
Template JSON Files
Tabula web-app accepts the user's drag & click as input and translates it into Java arguments that are actually used behind the scenes to parse PDF files. The translated Java arguments are accessible to users in a JSON format.
Select the area you want to parse, and click Save Selections as Template
. Then, Download
Cisco packet tracer 7 0 for mac free download. the translated Java arguments in a text JSON file. These arguments are useful when coding arguments for tabula.read_pdf()
later.
template.json
Running Tabula-py¶
Tabula-py enables you to extract tables from PDFs into DataFrame and JSON. It can also extract tables from PDFs and save files as CSV, TSV or JSON. Some basic code examples are as follows:
Area Selection
Epub To Pdf Converter Jpg
You can select portions of PDFs you want to analyze by setting area (top,left,bottom,right)
option in tabula.read_pdf()
. This is equivalent to dragging your mouse and setting the area of your interest in tabula web-app as it was mentioned above. Default is the entire page. Also note that you can choose the page, or pages you want to parse with pages
option.
The sample PDF file can be downloaded from here.
Start Date | End Date | (hr) | Activity | Activity Detail | Operation | Com | |
---|---|---|---|---|---|---|---|
0 | 12/13/2014r06:00 | 12/13/2014r09:00 | 3.0 | SURF-DRILL | DRILL SURFACE | DRL | Rotate from 1600' to 1859' (259' @ 8 fph). WOB. |
1 | 12/13/2014r09:00 | 12/13/2014r11:00 | 2.0 | SURF-CIRC | CIRCULATE | CIRC | Pump 2- 50 bbl hi vis sweep; Circulate to surface |
2 | 12/13/2014r11:00 | 12/13/2014r14:00 | 3.0 | SURF-TRIP | TOOH | TRIP | TOOH (Slick off bottom) f/1859' to 108' (SLM). |
3 | 12/13/2014r14:00 | 12/13/2014r16:00 | 2.0 | PLAN | EQUIP | BHA | PJSA - Break bit & L/D directional BHA, clean . |
4 | 12/13/2014r16:00 | 12/13/2014r17:30 | 1.5 | PLAN | DRLG | CSG | PTJSA / R/U Pipe Pros.Csg. tools / PTJSA on ru. |
5 | 12/13/2014r17:30 | 12/13/2014r18:00 | 0.5 | PLAN | DRLG | CSG | Make up 13 3/8 Gemco PDC drillable float shoe;. |
6 | 12/13/2014r18:00 | 12/13/2014r18:30 | 0.5 | PLAN | PERS | SFTY | HJSM with Morning tour crew, Pipe Pro casing c. |
7 | 12/13/2014r18:30 | 12/13/2014r23:30 | 5.0 | PLAN | DRLG | CSG | Make up 13 /8' PDC drillable float collar onto. |
8 | 12/13/2014r23:30 | 12/14/2014r01:30 | 2.0 | SURF-CIRC | CIRCULATE | CIRC | HJSM on Hoisting personal; Make up Swedge in . |
9 | 12/14/2014r01:30 | 12/14/2014r03:30 | 2.0 | PLAN | DRLG | CSG | Run 13 3/8'J-55 54.5 BTC f/ 1,639' to 1,819';. |
10 | 12/14/2014r03:30 | 12/14/2014r04:30 | 1.0 | SURF-CIRC | CIRCULATE | CIRC | Circulate Bttms up while Rigging down csg crew. |
11 | 12/14/2014r04:30 | 12/14/2014r06:00 | 1.5 | SURF-CMT | CEMENT SURFACErCASING | CMT | HJSM w/ Basic Cementer, H&P rig crew & PNR; D. |
Alternatively, you can set area with percentage scale by setting relative_area=True
. For this specific PDF file, the below area=(50, 5, 92, 100), relative_area=True
option is equivalent to area=(406, 24, 695, 589)
above.
Start Date | End Date | Dur (hr) | Activity | Activity Detail | Operation | Com | |
---|---|---|---|---|---|---|---|
0 | 2/13/2014r6:00 | 12/13/2014r09:00 | 3.0 | SURF-DRILL | DRILL SURFACE | DRL | Rotate from 1600' to 1859' (259' @ 8 fph). WOB. |
1 | 2/13/2014r9:00 | 12/13/2014r11:00 | 2.0 | SURF-CIRC | CIRCULATE | CIRC | Pump 2- 50 bbl hi vis sweep; Circulate to surface |
2 | 2/13/2014r1:00 | 12/13/2014r14:00 | 3.0 | SURF-TRIP | TOOH | TRIP | TOOH (Slick off bottom) f/1859' to 108' (SLM). |
3 | 2/13/2014r4:00 | 12/13/2014r16:00 | 2.0 | PLAN | EQUIP | BHA | PJSA - Break bit & L/D directional BHA, clean . |
4 | 2/13/2014r6:00 | 12/13/2014r17:30 | 1.5 | PLAN | DRLG | CSG | PTJSA / R/U Pipe Pros.Csg. tools / PTJSA on ru. |
5 | 2/13/2014r7:30 | 12/13/2014r18:00 | 0.5 | PLAN | DRLG | CSG | Make up 13 3/8 Gemco PDC drillable float shoe;. |
6 | 2/13/2014r8:00 | 12/13/2014r18:30 | 0.5 | PLAN | PERS | SFTY | HJSM with Morning tour crew, Pipe Pro casing c. |
7 | 2/13/2014r8:30 | 12/13/2014r23:30 | 5.0 | PLAN | DRLG | CSG | Make up 13 /8' PDC drillable float collar onto. |
8 | 2/13/2014r3:30 | 12/14/2014r01:30 | 2.0 | SURF-CIRC | CIRCULATE | CIRC | HJSM on Hoisting personal; Make up Swedge in . |
9 | 2/14/2014r1:30 | 12/14/2014r03:30 | 2.0 | PLAN | DRLG | CSG | Run 13 3/8'J-55 54.5 BTC f/ 1,639' to 1,819';. |
10 | 2/14/2014r3:30 | 12/14/2014r04:30 | 1.0 | SURF-CIRC | CIRCULATE | CIRC | Circulate Bttms up while Rigging down csg crew. |
11 | 2/14/2014r4:30 | 12/14/2014r06:00 | 1.5 | SURF-CMT | CEMENT SURFACErCASING | CMT | HJSM w/ Basic Cementer, H&P rig crew & PNR; D. |
Notes on Escape Characters
When used as lattice
mode, tabula replaces abnormally large spacing between texts and newline within a cell with r
. This can be fixed with a simple regex manipulation.
Alternatively, you can set area with percentage scale by setting relative_area=True
. For this specific PDF file, the below area=(50, 5, 92, 100), relative_area=True
option is equivalent to area=(406, 24, 695, 589)
above.
Start Date | End Date | Dur (hr) | Activity | Activity Detail | Operation | Com | |
---|---|---|---|---|---|---|---|
0 | 2/13/2014r6:00 | 12/13/2014r09:00 | 3.0 | SURF-DRILL | DRILL SURFACE | DRL | Rotate from 1600' to 1859' (259' @ 8 fph). WOB. |
1 | 2/13/2014r9:00 | 12/13/2014r11:00 | 2.0 | SURF-CIRC | CIRCULATE | CIRC | Pump 2- 50 bbl hi vis sweep; Circulate to surface |
2 | 2/13/2014r1:00 | 12/13/2014r14:00 | 3.0 | SURF-TRIP | TOOH | TRIP | TOOH (Slick off bottom) f/1859' to 108' (SLM). |
3 | 2/13/2014r4:00 | 12/13/2014r16:00 | 2.0 | PLAN | EQUIP | BHA | PJSA - Break bit & L/D directional BHA, clean . |
4 | 2/13/2014r6:00 | 12/13/2014r17:30 | 1.5 | PLAN | DRLG | CSG | PTJSA / R/U Pipe Pros.Csg. tools / PTJSA on ru. |
5 | 2/13/2014r7:30 | 12/13/2014r18:00 | 0.5 | PLAN | DRLG | CSG | Make up 13 3/8 Gemco PDC drillable float shoe;. |
6 | 2/13/2014r8:00 | 12/13/2014r18:30 | 0.5 | PLAN | PERS | SFTY | HJSM with Morning tour crew, Pipe Pro casing c. |
7 | 2/13/2014r8:30 | 12/13/2014r23:30 | 5.0 | PLAN | DRLG | CSG | Make up 13 /8' PDC drillable float collar onto. |
8 | 2/13/2014r3:30 | 12/14/2014r01:30 | 2.0 | SURF-CIRC | CIRCULATE | CIRC | HJSM on Hoisting personal; Make up Swedge in . |
9 | 2/14/2014r1:30 | 12/14/2014r03:30 | 2.0 | PLAN | DRLG | CSG | Run 13 3/8'J-55 54.5 BTC f/ 1,639' to 1,819';. |
10 | 2/14/2014r3:30 | 12/14/2014r04:30 | 1.0 | SURF-CIRC | CIRCULATE | CIRC | Circulate Bttms up while Rigging down csg crew. |
11 | 2/14/2014r4:30 | 12/14/2014r06:00 | 1.5 | SURF-CMT | CEMENT SURFACErCASING | CMT | HJSM w/ Basic Cementer, H&P rig crew & PNR; D. |
Notes on Escape Characters
When used as lattice
mode, tabula replaces abnormally large spacing between texts and newline within a cell with r
. This can be fixed with a simple regex manipulation.
Start Date | End Date | Dur (hr) | Activity | Activity Detail | Operation | Com | |
---|---|---|---|---|---|---|---|
0 | 2/13/2014 6:00 | 12/13/2014 09:00 | 3.0 | SURF-DRILL | DRILL SURFACE | DRL | Rotate from 1600' to 1859' (259' @ 8 fph). WOB. |
1 | 2/13/2014 9:00 | 12/13/2014 11:00 | 2.0 | SURF-CIRC | CIRCULATE | CIRC | Pump 2- 50 bbl hi vis sweep; Circulate to surface |
2 | 2/13/2014 1:00 | 12/13/2014 14:00 | 3.0 | SURF-TRIP | TOOH | TRIP | TOOH (Slick off bottom) f/1859' to 108' (SLM). |
3 | 2/13/2014 4:00 | 12/13/2014 16:00 | 2.0 | PLAN | EQUIP | BHA | PJSA - Break bit & L/D directional BHA, clean . |
4 | 2/13/2014 6:00 | 12/13/2014 17:30 | 1.5 | PLAN | DRLG | CSG | PTJSA / R/U Pipe Pros.Csg. tools / PTJSA on ru. |
5 | 2/13/2014 7:30 | 12/13/2014 18:00 | 0.5 | PLAN | DRLG | CSG | Make up 13 3/8 Gemco PDC drillable float shoe;. |
6 | 2/13/2014 8:00 | 12/13/2014 18:30 | 0.5 | PLAN | PERS | SFTY | HJSM with Morning tour crew, Pipe Pro casing c. |
7 | 2/13/2014 8:30 | 12/13/2014 23:30 | 5.0 | PLAN | DRLG | CSG | Make up 13 /8' PDC drillable float collar onto. |
8 | 2/13/2014 3:30 | 12/14/2014 01:30 | 2.0 | SURF-CIRC | CIRCULATE | CIRC | HJSM on Hoisting personal; Make up Swedge in . |
9 | 2/14/2014 1:30 | 12/14/2014 03:30 | 2.0 | PLAN | DRLG | CSG | Run 13 3/8'J-55 54.5 BTC f/ 1,639' to 1,819';. |
10 | 2/14/2014 3:30 | 12/14/2014 04:30 | 1.0 | SURF-CIRC | CIRCULATE | CIRC | Circulate Bttms up while Rigging down csg crew. |
11 | 2/14/2014 4:30 | 12/14/2014 06:00 | 1.5 | SURF-CMT | CEMENT SURFACE CASING | CMT | HJSM w/ Basic Cementer, H&P rig crew & PNR; D. |
Lattice Mode vs Stream Mode
Tabula supports two primary modes of table extraction — Lattice mode and Stream mode.
Lattice Mode
lattice=True
forces PDFs to be extracted using lattice-mode extraction. It recognizes each cells based on ruling lines, or borders of each cell.
Stream Mode
stream=True
forces PDFs to be extracted using stream-mode extraction. This mode is used when there are no ruling lines to differentiate one cell from the other. Instead, it uses spacings among each cells to recognize each cell.
PDF File 1: Lattice mode recommended
PDF file 2: Stream mode recommended
How would it look like if PDF File 1 and PDF file 2 are each extracted in both stream
mode and lattice
mode?
Start Date | End Date | (hr) | Activity | Activity Detail | Operation | Com | |
---|---|---|---|---|---|---|---|
0 | 12/13/2014r06:00 | 12/13/2014r09:00 | 3.0 | SURF-DRILL | DRILL SURFACE | DRL | Rotate from 1600' to 1859' (259' @ 8 fph). WOB. |
1 | 12/13/2014r09:00 | 12/13/2014r11:00 | 2.0 | SURF-CIRC | CIRCULATE | CIRC | Pump 2- 50 bbl hi vis sweep; Circulate to surface |
2 | 12/13/2014r11:00 | 12/13/2014r14:00 | 3.0 | SURF-TRIP | TOOH | TRIP | TOOH (Slick off bottom) f/1859' to 108' (SLM). |
3 | 12/13/2014r14:00 | 12/13/2014r16:00 | 2.0 | PLAN | EQUIP | BHA | PJSA - Break bit & L/D directional BHA, clean . |
4 | 12/13/2014r16:00 | 12/13/2014r17:30 | 1.5 | PLAN | DRLG | CSG | PTJSA / R/U Pipe Pros.Csg. tools / PTJSA on ru. |
Start Date | End Date | (hr) | Activity | Activity Detail | Operation | Com | |
---|---|---|---|---|---|---|---|
0 | 12/13/2014 | 12/13/2014 | 3.0 | SURF-DRILL | DRILL SURFACE | DRL | Rotate from 1600' to 1859' (259' @ 8 fph). WOB. |
1 | 06:00 | 09:00 | NaN | NaN | NaN | NaN | SPP 2300, motor diff 650, 800 GPM, torque 18k. |
2 | NaN | NaN | NaN | NaN | NaN | NaN | (T.D. Surface @ 09:00 12-13-14) |
3 | 12/13/2014 | 12/13/2014 | 2.0 | SURF-CIRC | CIRCULATE | CIRC | Pump 2- 50 bbl hi vis sweep; Circulate to surface |
4 | 09:00 | 11:00 | NaN | NaN | NaN | NaN | NaN |
5 | 12/13/2014 | 12/13/2014 | 3.0 | SURF-TRIP | TOOH | TRIP | TOOH (Slick off bottom) f/1859' to 108' (SLM). |
6 | 11:00 | 14:00 | NaN | NaN | NaN | NaN | Hole taking correct fill |
7 | 12/13/2014 | 12/13/2014 | 2.0 | PLAN | EQUIP | BHA | PJSA - Break bit & L/D directional BHA, clean . |
8 | 14:00 | 16:00 | NaN | NaN | NaN | NaN | ext. |
9 | 12/13/2014 | 12/13/2014 | 1.5 | PLAN | DRLG | CSG | PTJSA / R/U Pipe Pros.Csg. tools / PTJSA on ru. |
10 | 16:00 | 17:30 | NaN | NaN | NaN | NaN | csg. |
Pdf To Epub Converter 6 2 13 Inch
Unnamed: 0 | WELL INFORMATION | |
---|---|---|
0 | API No.: 42-003-46352 | County: A |
1 | Well No.:22H | RRC Distri |
2 | Lease Name: UNIVERSITY '7-43' | Field Name |
3 | RRC Lease No.: 40532 | Field No.: |
4 | Location: Section: 35, Block: 7, Survey: UN. | NaN |
5 | Latitude: | Longitude: |
6 | This well is located 17.2 | miles in a SE |
7 | direction from ANDREWS, | NaN |
8 | which is the nearest town in the county. | NaN |
Pdf Converter To Epub
Observe how lattice
mode extraction for PDF file 2 was able to extract only 'WELL INFORMATION' string. This is not an error. Recall that lattice
mode identifies cells by ruling lines.
Notes About guess
option
According to the offical documentation, guess
is known to make a conflict between stream
option. If you feel something strange with your result, try setting guess=False
.
For example, for PDF File 1, if stream
mode is used without setting guess=False
, it would look like this:
Report #:3 | Daily Operation:12/13/2014 06:00 - 12/14/2014 06:00 | Unnamed: 2 | Unnamed: 3 | Unnamed: 4 | Unnamed: 5 | Unnamed: 6 | |
---|---|---|---|---|---|---|---|
0 | Job Category | NaN | Primary Job Type | NaN | NaN | AFE Number | NaN |
1 | ORIG DRILLING | NaN | ODR | NaN | NaN | 033402 | NaN |
2 | Days From Spud (days) | Days on Location (days) | End Depth (ftKB) End Depth (TVD) (ftKB) | Dens Last Mud (lb/gal) | Rig | NaN | NaN |
3 | 1 | 3 | 1,859.0 1,858.5 | 8.60 | H & P, 637 | NaN | NaN |
4 | Operations Summary | NaN | NaN | NaN | NaN | NaN | NaN |
5 | Drld. Surface f/1600' to 1859' T.D. @ 09:00. | NaN | NaN | NaN | NaN | NaN | NaN |
6 | S/M, R/U csg running equip & Run 45 jts. of. | NaN | NaN | NaN | NaN | NaN | NaN |
7 | Surface Float shoe @ 1,857.5' | NaN | NaN | NaN | NaN | NaN | Surface |
8 | Float collar @ 1,817.9' | NaN | NaN | NaN | NaN | NaN | NaN |
9 | Remarks | NaN | NaN | NaN | NaN | NaN | NaN |
10 | Rig (H&P 637), Well (University 7-43 # 22H) | NaN | NaN | NaN | NaN | NaN | NaN |
Pandas Option
Pandas arguments can be passed into tabula.read_pdf()
as a dictionary object.
0 | 1 | 2 | 3 | 4 | 5 | 6 | |
---|---|---|---|---|---|---|---|
0 | Start Date | End Date | (hr) | Activity | Activity Detail | Operation | Com |
1 | 12/13/2014r06:00 | 12/13/2014r09:00 | 3 | SURF-DRILL | DRILL SURFACE | DRL | Rotate from 1600' to 1859' (259' @ 8 fph). WOB. |
2 | 12/13/2014r09:00 | 12/13/2014r11:00 | 2 | SURF-CIRC | CIRCULATE | CIRC | Pump 2- 50 bbl hi vis sweep; Circulate to surface |
3 | 12/13/2014r11:00 | 12/13/2014r14:00 | 3 | SURF-TRIP | TOOH | TRIP | TOOH (Slick off bottom) f/1859' to 108' (SLM). |
4 | 12/13/2014r14:00 | 12/13/2014r16:00 | 2 | PLAN | EQUIP | BHA | PJSA - Break bit & L/D directional BHA, clean . |
More Documentation¶
Further instructions about tabula-py can be found on its official github repo.
Related Posts
Understanding Multi-Dimensionality in Vector Space Modeling
How does word vectors in Natural Language Processing capture meaningful relationships among words? How can you quantify those relationships? Addressing these questions starts from understanding the multi-dimensional nature of NLP applications. Schwartz 1 8.
Demystifying Neural Network in Skip-Gram Language Modeling
The past couple of years, neural networks in Word2Vec have nearly taken over the field of NLP, thanks to their state-of-art performance. But how much do you understand about the algorithm behind it? This post will crack the secrets behind neural net in Word2Vec.
Optimize Computational Efficiency of Skip-Gram with Negative Sampling
When training your NLP model with Skip-Gram, the very large size of vocabs imposes high computational cost on your machine. Since the original Skip-Gram model is unable to handle this high cost, we use an alternative, called Negative Sampling.