Week1 Notes

What a Code Book should contain 1) information about variables in the data set not contained in the tidy data 2) Information about the summary choices made 3) Information about the experimental study design used

A common format: Word/text file There should be a section called “Study Design” that has a through description of how you collected data.

The instruction list - Ideally in R script - The input is raw data - The output is the processed, tidy data - There are no parameters to the script

Get/set working directory -In Mac OS:

setwd("./data")

-In Windows

setwd("C:\\Users\\Andrew\\Downloads")

Checking for and creating directories

if (!file.exists("data")){
    dir.create("data")
}

Getting data from the Internet

download.file(url = , destfile = , )

An example of downloading datat form baltimorecity website

list.files("./data")

[1] "cameras.csv"

How to open local file - I downloaded the Baltimore fixed camera dataset mannually and save it in the file in “./data/Fixed_Speed_Cameras.csv”

Now try to read it!

Some important parameters quote - sometimes we should set quoted="" na.strings - set the character that repressent a missing value nrows - how many rows to read skip - number of lines to skip befere starting to read

read Excel files

library(xlsx)
camrraData2 <- read.xlsx("./data/xxx.xlsx",sheetIndex = 1, header = TRUE)

• read.xlxs2 is much faster than read.xlsx but for reading subsets of rows may be slightly unstable

• XLConnect package has more options for writing and manipulating Excel files

• XLCnonnect cignette is a good place to start for that package

Reading XML

1)Tags, elements and attributes Tages - Start tages

• End tages

  - Empty tags<line-break />

Elements - Hello, world Attributes are componets of the label - alt=“instructor”/> - Connect A to B.

Get the items on the menu and prices

xpathApply(rootNode"//name",xmlValue)
xpathApply(rootNode"//price",xmlValue)

doc <- htmlTreeParse(myUrl, useInternal = TRUE)

Warning: XML content does not seem to be XML: ''

Reading Javascript Object Notation(JSON) - Lightweight data storage

jsonDATA$owner$login

[1] "Zixuan-YU" "Zixuan-YU" "Zixuan-YU" "Zixuan-YU"

Writing data frames to JSON

cat(myjson)

[
  {
    "Sepal.Length": 5.1,
    "Sepal.Width": 3.5,
    "Petal.Length": 1.4,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 4.9,
    "Sepal.Width": 3,
    "Petal.Length": 1.4,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 4.7,
    "Sepal.Width": 3.2,
    "Petal.Length": 1.3,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 4.6,
    "Sepal.Width": 3.1,
    "Petal.Length": 1.5,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5,
    "Sepal.Width": 3.6,
    "Petal.Length": 1.4,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5.4,
    "Sepal.Width": 3.9,
    "Petal.Length": 1.7,
    "Petal.Width": 0.4,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 4.6,
    "Sepal.Width": 3.4,
    "Petal.Length": 1.4,
    "Petal.Width": 0.3,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5,
    "Sepal.Width": 3.4,
    "Petal.Length": 1.5,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 4.4,
    "Sepal.Width": 2.9,
    "Petal.Length": 1.4,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 4.9,
    "Sepal.Width": 3.1,
    "Petal.Length": 1.5,
    "Petal.Width": 0.1,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5.4,
    "Sepal.Width": 3.7,
    "Petal.Length": 1.5,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 4.8,
    "Sepal.Width": 3.4,
    "Petal.Length": 1.6,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 4.8,
    "Sepal.Width": 3,
    "Petal.Length": 1.4,
    "Petal.Width": 0.1,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 4.3,
    "Sepal.Width": 3,
    "Petal.Length": 1.1,
    "Petal.Width": 0.1,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5.8,
    "Sepal.Width": 4,
    "Petal.Length": 1.2,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5.7,
    "Sepal.Width": 4.4,
    "Petal.Length": 1.5,
    "Petal.Width": 0.4,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5.4,
    "Sepal.Width": 3.9,
    "Petal.Length": 1.3,
    "Petal.Width": 0.4,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5.1,
    "Sepal.Width": 3.5,
    "Petal.Length": 1.4,
    "Petal.Width": 0.3,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5.7,
    "Sepal.Width": 3.8,
    "Petal.Length": 1.7,
    "Petal.Width": 0.3,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5.1,
    "Sepal.Width": 3.8,
    "Petal.Length": 1.5,
    "Petal.Width": 0.3,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5.4,
    "Sepal.Width": 3.4,
    "Petal.Length": 1.7,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5.1,
    "Sepal.Width": 3.7,
    "Petal.Length": 1.5,
    "Petal.Width": 0.4,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 4.6,
    "Sepal.Width": 3.6,
    "Petal.Length": 1,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5.1,
    "Sepal.Width": 3.3,
    "Petal.Length": 1.7,
    "Petal.Width": 0.5,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 4.8,
    "Sepal.Width": 3.4,
    "Petal.Length": 1.9,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5,
    "Sepal.Width": 3,
    "Petal.Length": 1.6,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5,
    "Sepal.Width": 3.4,
    "Petal.Length": 1.6,
    "Petal.Width": 0.4,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5.2,
    "Sepal.Width": 3.5,
    "Petal.Length": 1.5,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5.2,
    "Sepal.Width": 3.4,
    "Petal.Length": 1.4,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 4.7,
    "Sepal.Width": 3.2,
    "Petal.Length": 1.6,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 4.8,
    "Sepal.Width": 3.1,
    "Petal.Length": 1.6,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5.4,
    "Sepal.Width": 3.4,
    "Petal.Length": 1.5,
    "Petal.Width": 0.4,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5.2,
    "Sepal.Width": 4.1,
    "Petal.Length": 1.5,
    "Petal.Width": 0.1,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5.5,
    "Sepal.Width": 4.2,
    "Petal.Length": 1.4,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 4.9,
    "Sepal.Width": 3.1,
    "Petal.Length": 1.5,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5,
    "Sepal.Width": 3.2,
    "Petal.Length": 1.2,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5.5,
    "Sepal.Width": 3.5,
    "Petal.Length": 1.3,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 4.9,
    "Sepal.Width": 3.6,
    "Petal.Length": 1.4,
    "Petal.Width": 0.1,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 4.4,
    "Sepal.Width": 3,
    "Petal.Length": 1.3,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5.1,
    "Sepal.Width": 3.4,
    "Petal.Length": 1.5,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5,
    "Sepal.Width": 3.5,
    "Petal.Length": 1.3,
    "Petal.Width": 0.3,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 4.5,
    "Sepal.Width": 2.3,
    "Petal.Length": 1.3,
    "Petal.Width": 0.3,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 4.4,
    "Sepal.Width": 3.2,
    "Petal.Length": 1.3,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5,
    "Sepal.Width": 3.5,
    "Petal.Length": 1.6,
    "Petal.Width": 0.6,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5.1,
    "Sepal.Width": 3.8,
    "Petal.Length": 1.9,
    "Petal.Width": 0.4,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 4.8,
    "Sepal.Width": 3,
    "Petal.Length": 1.4,
    "Petal.Width": 0.3,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5.1,
    "Sepal.Width": 3.8,
    "Petal.Length": 1.6,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 4.6,
    "Sepal.Width": 3.2,
    "Petal.Length": 1.4,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5.3,
    "Sepal.Width": 3.7,
    "Petal.Length": 1.5,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 5,
    "Sepal.Width": 3.3,
    "Petal.Length": 1.4,
    "Petal.Width": 0.2,
    "Species": "setosa"
  },
  {
    "Sepal.Length": 7,
    "Sepal.Width": 3.2,
    "Petal.Length": 4.7,
    "Petal.Width": 1.4,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 6.4,
    "Sepal.Width": 3.2,
    "Petal.Length": 4.5,
    "Petal.Width": 1.5,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 6.9,
    "Sepal.Width": 3.1,
    "Petal.Length": 4.9,
    "Petal.Width": 1.5,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 5.5,
    "Sepal.Width": 2.3,
    "Petal.Length": 4,
    "Petal.Width": 1.3,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 6.5,
    "Sepal.Width": 2.8,
    "Petal.Length": 4.6,
    "Petal.Width": 1.5,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 5.7,
    "Sepal.Width": 2.8,
    "Petal.Length": 4.5,
    "Petal.Width": 1.3,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 6.3,
    "Sepal.Width": 3.3,
    "Petal.Length": 4.7,
    "Petal.Width": 1.6,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 4.9,
    "Sepal.Width": 2.4,
    "Petal.Length": 3.3,
    "Petal.Width": 1,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 6.6,
    "Sepal.Width": 2.9,
    "Petal.Length": 4.6,
    "Petal.Width": 1.3,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 5.2,
    "Sepal.Width": 2.7,
    "Petal.Length": 3.9,
    "Petal.Width": 1.4,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 5,
    "Sepal.Width": 2,
    "Petal.Length": 3.5,
    "Petal.Width": 1,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 5.9,
    "Sepal.Width": 3,
    "Petal.Length": 4.2,
    "Petal.Width": 1.5,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 6,
    "Sepal.Width": 2.2,
    "Petal.Length": 4,
    "Petal.Width": 1,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 6.1,
    "Sepal.Width": 2.9,
    "Petal.Length": 4.7,
    "Petal.Width": 1.4,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 5.6,
    "Sepal.Width": 2.9,
    "Petal.Length": 3.6,
    "Petal.Width": 1.3,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 6.7,
    "Sepal.Width": 3.1,
    "Petal.Length": 4.4,
    "Petal.Width": 1.4,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 5.6,
    "Sepal.Width": 3,
    "Petal.Length": 4.5,
    "Petal.Width": 1.5,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 5.8,
    "Sepal.Width": 2.7,
    "Petal.Length": 4.1,
    "Petal.Width": 1,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 6.2,
    "Sepal.Width": 2.2,
    "Petal.Length": 4.5,
    "Petal.Width": 1.5,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 5.6,
    "Sepal.Width": 2.5,
    "Petal.Length": 3.9,
    "Petal.Width": 1.1,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 5.9,
    "Sepal.Width": 3.2,
    "Petal.Length": 4.8,
    "Petal.Width": 1.8,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 6.1,
    "Sepal.Width": 2.8,
    "Petal.Length": 4,
    "Petal.Width": 1.3,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 6.3,
    "Sepal.Width": 2.5,
    "Petal.Length": 4.9,
    "Petal.Width": 1.5,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 6.1,
    "Sepal.Width": 2.8,
    "Petal.Length": 4.7,
    "Petal.Width": 1.2,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 6.4,
    "Sepal.Width": 2.9,
    "Petal.Length": 4.3,
    "Petal.Width": 1.3,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 6.6,
    "Sepal.Width": 3,
    "Petal.Length": 4.4,
    "Petal.Width": 1.4,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 6.8,
    "Sepal.Width": 2.8,
    "Petal.Length": 4.8,
    "Petal.Width": 1.4,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 6.7,
    "Sepal.Width": 3,
    "Petal.Length": 5,
    "Petal.Width": 1.7,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 6,
    "Sepal.Width": 2.9,
    "Petal.Length": 4.5,
    "Petal.Width": 1.5,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 5.7,
    "Sepal.Width": 2.6,
    "Petal.Length": 3.5,
    "Petal.Width": 1,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 5.5,
    "Sepal.Width": 2.4,
    "Petal.Length": 3.8,
    "Petal.Width": 1.1,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 5.5,
    "Sepal.Width": 2.4,
    "Petal.Length": 3.7,
    "Petal.Width": 1,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 5.8,
    "Sepal.Width": 2.7,
    "Petal.Length": 3.9,
    "Petal.Width": 1.2,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 6,
    "Sepal.Width": 2.7,
    "Petal.Length": 5.1,
    "Petal.Width": 1.6,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 5.4,
    "Sepal.Width": 3,
    "Petal.Length": 4.5,
    "Petal.Width": 1.5,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 6,
    "Sepal.Width": 3.4,
    "Petal.Length": 4.5,
    "Petal.Width": 1.6,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 6.7,
    "Sepal.Width": 3.1,
    "Petal.Length": 4.7,
    "Petal.Width": 1.5,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 6.3,
    "Sepal.Width": 2.3,
    "Petal.Length": 4.4,
    "Petal.Width": 1.3,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 5.6,
    "Sepal.Width": 3,
    "Petal.Length": 4.1,
    "Petal.Width": 1.3,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 5.5,
    "Sepal.Width": 2.5,
    "Petal.Length": 4,
    "Petal.Width": 1.3,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 5.5,
    "Sepal.Width": 2.6,
    "Petal.Length": 4.4,
    "Petal.Width": 1.2,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 6.1,
    "Sepal.Width": 3,
    "Petal.Length": 4.6,
    "Petal.Width": 1.4,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 5.8,
    "Sepal.Width": 2.6,
    "Petal.Length": 4,
    "Petal.Width": 1.2,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 5,
    "Sepal.Width": 2.3,
    "Petal.Length": 3.3,
    "Petal.Width": 1,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 5.6,
    "Sepal.Width": 2.7,
    "Petal.Length": 4.2,
    "Petal.Width": 1.3,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 5.7,
    "Sepal.Width": 3,
    "Petal.Length": 4.2,
    "Petal.Width": 1.2,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 5.7,
    "Sepal.Width": 2.9,
    "Petal.Length": 4.2,
    "Petal.Width": 1.3,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 6.2,
    "Sepal.Width": 2.9,
    "Petal.Length": 4.3,
    "Petal.Width": 1.3,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 5.1,
    "Sepal.Width": 2.5,
    "Petal.Length": 3,
    "Petal.Width": 1.1,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 5.7,
    "Sepal.Width": 2.8,
    "Petal.Length": 4.1,
    "Petal.Width": 1.3,
    "Species": "versicolor"
  },
  {
    "Sepal.Length": 6.3,
    "Sepal.Width": 3.3,
    "Petal.Length": 6,
    "Petal.Width": 2.5,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 5.8,
    "Sepal.Width": 2.7,
    "Petal.Length": 5.1,
    "Petal.Width": 1.9,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 7.1,
    "Sepal.Width": 3,
    "Petal.Length": 5.9,
    "Petal.Width": 2.1,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6.3,
    "Sepal.Width": 2.9,
    "Petal.Length": 5.6,
    "Petal.Width": 1.8,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6.5,
    "Sepal.Width": 3,
    "Petal.Length": 5.8,
    "Petal.Width": 2.2,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 7.6,
    "Sepal.Width": 3,
    "Petal.Length": 6.6,
    "Petal.Width": 2.1,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 4.9,
    "Sepal.Width": 2.5,
    "Petal.Length": 4.5,
    "Petal.Width": 1.7,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 7.3,
    "Sepal.Width": 2.9,
    "Petal.Length": 6.3,
    "Petal.Width": 1.8,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6.7,
    "Sepal.Width": 2.5,
    "Petal.Length": 5.8,
    "Petal.Width": 1.8,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 7.2,
    "Sepal.Width": 3.6,
    "Petal.Length": 6.1,
    "Petal.Width": 2.5,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6.5,
    "Sepal.Width": 3.2,
    "Petal.Length": 5.1,
    "Petal.Width": 2,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6.4,
    "Sepal.Width": 2.7,
    "Petal.Length": 5.3,
    "Petal.Width": 1.9,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6.8,
    "Sepal.Width": 3,
    "Petal.Length": 5.5,
    "Petal.Width": 2.1,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 5.7,
    "Sepal.Width": 2.5,
    "Petal.Length": 5,
    "Petal.Width": 2,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 5.8,
    "Sepal.Width": 2.8,
    "Petal.Length": 5.1,
    "Petal.Width": 2.4,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6.4,
    "Sepal.Width": 3.2,
    "Petal.Length": 5.3,
    "Petal.Width": 2.3,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6.5,
    "Sepal.Width": 3,
    "Petal.Length": 5.5,
    "Petal.Width": 1.8,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 7.7,
    "Sepal.Width": 3.8,
    "Petal.Length": 6.7,
    "Petal.Width": 2.2,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 7.7,
    "Sepal.Width": 2.6,
    "Petal.Length": 6.9,
    "Petal.Width": 2.3,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6,
    "Sepal.Width": 2.2,
    "Petal.Length": 5,
    "Petal.Width": 1.5,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6.9,
    "Sepal.Width": 3.2,
    "Petal.Length": 5.7,
    "Petal.Width": 2.3,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 5.6,
    "Sepal.Width": 2.8,
    "Petal.Length": 4.9,
    "Petal.Width": 2,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 7.7,
    "Sepal.Width": 2.8,
    "Petal.Length": 6.7,
    "Petal.Width": 2,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6.3,
    "Sepal.Width": 2.7,
    "Petal.Length": 4.9,
    "Petal.Width": 1.8,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6.7,
    "Sepal.Width": 3.3,
    "Petal.Length": 5.7,
    "Petal.Width": 2.1,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 7.2,
    "Sepal.Width": 3.2,
    "Petal.Length": 6,
    "Petal.Width": 1.8,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6.2,
    "Sepal.Width": 2.8,
    "Petal.Length": 4.8,
    "Petal.Width": 1.8,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6.1,
    "Sepal.Width": 3,
    "Petal.Length": 4.9,
    "Petal.Width": 1.8,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6.4,
    "Sepal.Width": 2.8,
    "Petal.Length": 5.6,
    "Petal.Width": 2.1,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 7.2,
    "Sepal.Width": 3,
    "Petal.Length": 5.8,
    "Petal.Width": 1.6,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 7.4,
    "Sepal.Width": 2.8,
    "Petal.Length": 6.1,
    "Petal.Width": 1.9,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 7.9,
    "Sepal.Width": 3.8,
    "Petal.Length": 6.4,
    "Petal.Width": 2,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6.4,
    "Sepal.Width": 2.8,
    "Petal.Length": 5.6,
    "Petal.Width": 2.2,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6.3,
    "Sepal.Width": 2.8,
    "Petal.Length": 5.1,
    "Petal.Width": 1.5,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6.1,
    "Sepal.Width": 2.6,
    "Petal.Length": 5.6,
    "Petal.Width": 1.4,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 7.7,
    "Sepal.Width": 3,
    "Petal.Length": 6.1,
    "Petal.Width": 2.3,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6.3,
    "Sepal.Width": 3.4,
    "Petal.Length": 5.6,
    "Petal.Width": 2.4,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6.4,
    "Sepal.Width": 3.1,
    "Petal.Length": 5.5,
    "Petal.Width": 1.8,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6,
    "Sepal.Width": 3,
    "Petal.Length": 4.8,
    "Petal.Width": 1.8,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6.9,
    "Sepal.Width": 3.1,
    "Petal.Length": 5.4,
    "Petal.Width": 2.1,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6.7,
    "Sepal.Width": 3.1,
    "Petal.Length": 5.6,
    "Petal.Width": 2.4,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6.9,
    "Sepal.Width": 3.1,
    "Petal.Length": 5.1,
    "Petal.Width": 2.3,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 5.8,
    "Sepal.Width": 2.7,
    "Petal.Length": 5.1,
    "Petal.Width": 1.9,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6.8,
    "Sepal.Width": 3.2,
    "Petal.Length": 5.9,
    "Petal.Width": 2.3,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6.7,
    "Sepal.Width": 3.3,
    "Petal.Length": 5.7,
    "Petal.Width": 2.5,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6.7,
    "Sepal.Width": 3,
    "Petal.Length": 5.2,
    "Petal.Width": 2.3,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6.3,
    "Sepal.Width": 2.5,
    "Petal.Length": 5,
    "Petal.Width": 1.9,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6.5,
    "Sepal.Width": 3,
    "Petal.Length": 5.2,
    "Petal.Width": 2,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 6.2,
    "Sepal.Width": 3.4,
    "Petal.Length": 5.4,
    "Petal.Width": 2.3,
    "Species": "virginica"
  },
  {
    "Sepal.Length": 5.9,
    "Sepal.Width": 3,
    "Petal.Length": 5.1,
    "Petal.Width": 1.8,
    "Species": "virginica"
  }
]

Convert back to JSON

More informations about JSON: 1) http://www.json.org/ 2) tutorail: http://www.r-bloggers.com/new-package-jsonlite-a-smarter-json-encoderdecoder/ 3) jsonlite vignette

Data.table 1) written in C and much faster 2) all functions accept data.frame work on data.table

tables()

   NAME NROW NCOL MB  COLS KEY
1:   DT    9    3  0 x,y,z    
Total: 0MB

#see all the data tables in memory

subsetting rows

subsetting rows

subsetting columns!! DIFFERENT

k = {print(10); 5}

[1] 10

print(k)

[1] 5

Calculating values for variables with expressions

DT[,table(y)]

y
a b c 
3 3 3 

Adding new columns, using “:=”

Multiple operations

DT[,m:={tmp <-(x+z); log2(tmp+5)}]

Error in `:=`(m, { : 
  Check that is.data.table(DT) == TRUE. Otherwise, := and `:=`(...) are defined for use in j, once only and in particular ways. See help(":=").

plyr like operations

Sepcial Variables .N An integer, lenth 1, containing the number

Keys

Joins

Fast Reading

system.time(fread(file))

   user  system elapsed 
  0.089   0.016   0.105 

system.time(read.table(file, header = TRUE, sep = "\t"))

   user  system elapsed 
  5.392   0.110   5.529 

the differences with df and dt: https://stackoverflow.com/questions/13618488/what-you-can-do-with-a-data-frame-that-you-cant-with-a-data-table

When you save the notebook, an HTML file containing the code and output will be saved alongside it (click the Preview button or press Cmd+Shift+K to preview the HTML file).

The preview shows you a rendered HTML copy of the contents of the editor. Consequently, unlike Knit, Preview does not run any R code chunks. Instead, the output of the chunk when it was last run in the editor is displayed.