Note: Vimcast

11 Jul 2014

Converting between tabs and spaces

:retab!

Delete blank lines

:g/^$/d

Close all other windows

:on[ly]

Move windows

ctrl-w r    " rotate all windows
ctrl-w R    " reversely rotate
ctrl-w x    " extrange current window with its neighbour
ctrl-w [HJKL]

Command-T auto flush

ctrl-f

Pathogen + Git submodules

git submodule init
git submodule update

Changelist

g; " jump back
g, " jump forwards
:changes

Jumplist

ctrl-o " back
ctrl-i " forward
ctrl-] " follow link in help

Visual Block

ctrl-v " like visual mode but select a block
:s/\%V_/ /g " match only on the selected block

Implicit motion command	Longhand equivalent
c{motion}	d{motion}i
C	d$a
s	xi
S	^C
I	^i

File Explorer

lazy	open file explorer
`:e.`	at current working directory
`:E`	at directory of current file

Manipulating the filesystem

command	action
%	create a new file
d	create a new directory
R	rename the file/directory
D	delete the file/directory

Spell Checking

:set spell to toggle it on and off
]s to proceed to the next error
[s previous error
z= get a list of suggested corrections
zg add a word to the spellfile
zw remove a word from the spelling dictionary

Ruby Style Guide

29 Jun 2014

%w(literal string array)

%i(literal symbol array)

Use Hash#fetch. It will raise a KeyError, making the problem obvious

Object#to_s method is invoked automatically when it’s interpolated object.

eg: message = "This is the #{object}."

Use String#<<, it mutates the original string and is faster

String#+ will create a new string

Create a symbol with spaces in it :"some string"

####Questions

What’s the meaning that Ruby 1.9 hashes are ordered

Notes: Working Effectively with Legacy Code

17 Jun 2014

To some degree, when we are adding behavior to the system, we are also changing behavior(load time, UI, etc)

RP: Week 1

10 Jun 2014

####Basic atomic classes of objects

character
numeric
integer
complex
logical

####Vector vs List

Vector: objects of the same class

vector(<class>, <length>)

List: can contain objects of different classes

####Numbers

default double precision real number
1L-> explicitly integer 1
Inf

1 / 0 = Inf 1 / Inf = 0
NaN: not a number

0 / 0 = NaN

####Attributes

names, dimnames
dimensions
class
length
other user-defined attributes/metadata
attributes()

####Assignment

<-

####Integer sequence

1:20

####Creating vectors

c(0.5, 0.6)
vector(“numeric”, length = 10)

####Explicit coercion

as.class function
Nonsensical coercion results in NAs

####Matrices

dim()

return nrow, ncol
it’s constructed column-wise
creating from vector
```
  m <- 1:10
  dim(m) <- c(2,5)
```
creating by column-binding or row-binding
```
  cbind()
  rbind()
```

####Factors

labels
levels

####Missing values

NA
NaN
is.na()
is.nan()
NA values have a class too.
NaN is NA
NA is not NaN

####Data frames

row.names
read.table() or read.csv()
data.matrix()

####Names

R objects can have names

names()

List elements can also have names

dimnames()

###Subsetting

[]
[[]]
$

####Subsetting a Matrix

drop = FALSE will result in a matrix otherwise will result in a vector(in most case)

####Partial matching

x<-list(aardvark=1:5)
x$a #aardvark
x[["a", exact = FALSE]]

####Reading and writing data

dput: single object
dump: multiple objects

RSpec: Notes

09 Jun 2014

####Modifier vs Matcher

Modifier eg: should, should_not Matcher eg: <, ==, >

####Predicate matcher

class Zombie
  def hungry?
    true
  end
end

Zombie.new.should be_hungry

####Pending

it "nothing"

xit "something" do
  # ...
end

it "something" do
  pending
  # ...
end

Luqi Pan