RPR-Data-Import

Importing data in R

(Data import from unstructured text, structured text, spreadsheets, online repositories, and Web pages)

 

Abstract:

Practical for data import from text files, spreadsheets and Web pages.

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Objectives: ...

Outcomes: ...

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Deliverables:

• Time management: Before you begin, estimate how long it will take you to complete this unit. Then, record in your course journal: the number of hours you estimated, the number of hours you worked on the unit, and the amount of time that passed between start and completion of this unit.
• Journal: Document your progress in your Course Journal. Some tasks may ask you to include specific items in your journal. Don't overlook these.
• Insights: If you find something particularly noteworthy about this unit, make a note in your insights! page.

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Prerequisites:

• RPR-Introduction (Introduction to R)

 

 

 

Contents

• Line endings
• Unstructured text files, headers, skip, omit, and rownames
• Caution with stringsAsFactors
• Caution with coerced data
• Text files with keywords
• Text-files: changing state
• Text-files: csv and tsv (and Excel sheets)
• Text-files: slurping, chunking and streaming
• curl
• httr GET and POST
• XML - libraries and cpath
• Binary Data
• R objects: save() and load()

Regex for screenscraping example:

Screenscraping

Write a PHP program that screenscrapes resolution data for a protein structure file from the PDB.

 Here is a link to a PDB record to illustrate the URL format.

Solution

   Fetch the contents of the URL into a string. Use a regex that captures the data you want to retrieve as part of some unique pattern in the HTML source. Print.

   ;The regex:

:/\s*(\d+\.\d+)/ *   identifying tag for the information we are looking for, ...

   *\s*   ... probably followed by whitespace, ...
   *(\d+\.\d+)   ... the "payload" of the match: one or more digits, a literal dot and and one or more digits.

   ;The code:
   <source lang="PHP">
   <?php
 $URLpath = "http://www.pdb.org/pdb/explore/explore.do?structureId=";
 $PDBid = "2imm";
 $source = file_get_contents($URLpath . $PDBid);

preg_match('/\s*?(\d+\.\d+)/', $source, $resolution);

 print($resolution[1]);
 ?>

Self-evaluation

Notes

Further reading, links and resources

 

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If in doubt, ask! If anything about this learning unit is not clear to you, do not proceed blindly but ask for clarification. Post your question on the course mailing list: others are likely to have similar problems. Or send an email to your instructor.

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About ...
 
Author:

Boris Steipe <boris.steipe@utoronto.ca>

Created:

2017-09-17

Modified:

2018-01-31

Version:

1.0

Version history:

• 1.0 first live version
• 0.2 Contents outline
• 0.1 First stub

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