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Cards (114)
Section 1
(50 cards)
paste0( )
a calling sequence eliminating spaces
factor
a special type of vector for categorical data
data frame
often stores datasets. A special type of list that is more general than a matrix. A two dimensional array with columns of vectors of the same length, but possibly of different types. Can be created using the data.frame( ) command. Variables can be accessed using the $.
cbind( )
yields a matrix object with columns specified
sum( )
count of the elements meeting the condition
character vector
the most complex type of atomic vector. Each element is a string, which can be an arbitrary amount of data.
rbind( )
yields a matrix object with rows specified
include=FALSE
option that omits R code and results
double vectors
belongs to the numeric class; the default type of number in R.
list
several vectors having the same length, but possibly having different data types
```{r ChunkName1} ```
option that names code chunk
typeof( )
provides information about the underlying data structure of objects (i.e. logical, integer, double, complex, character, list).
exists function
conveys whether an object exists in the workspace
logical vectors
simplest type of atomic vector; three possible values: TRUE, FALSE, or NA
library( )
a function that will load an installed package
recursive vectors
another word for list, meaning that lists can contain other lists
replicability
the same person (or different people) getting the same results using different data
attributes( )
displays the attributes associated with an object
rm command
removes an object in the workspace
*sentence*: the square root of 77 is `r sqrt(77)` first <- "Foo" last <- "Fu" *sentence*: the bunny's name is paste(first, last)
How to say "The square root of 77 is 8.775" and/or The bunny is named Foo Fu
data science
a combination of statistics, computer science, and mathematics that focuses on extracting meaningful information from data from a specific domain.
install.packages( )
a function used to download/install packages
vector
a one-dimensional array of items of the same data type (homogeneous)
position
(numerical) where in relation to other things?
object
something stored in R's memory; created using the <- or = assignment
message=FALSE or warning=FALSE
option that suppresses messages/warnings in output
paste( )
a calling sequence
eval=FALSE
option that does not run a code chunk, but displays the code
reproducibility
the same person (or different people) getting the same results using the same data
results='hide' or fig.show='hide'
option that runs a code chunk but suppresses output
unlist( )
a function that flattens (or makes a vector out of) the elements in a list; coerces objects into a common type.
prompt=TRUE
option that shows > prompt in front of commands
[ ]
extracts a sub-list
angle
(numerical) how wide? parallel to something else?
str( )
provides information about the structure of each object
"Environment" tab
shows the names (and values) of all the objects that exist in the current workspace
length
(numerical) how big (in one dimension)?
collapse=TRUE
option that compresses code and results in the chunk output
data.frame
Where data sets are often stored; special type of list that is more general than a matrix. A two-dimensional array with columns of vectors of the same length, but of possibly different types.
Visual cues
1) Position 2) Length 3) Angle 4) Direction 5) Shape 6) Area 7) Volume 8) Color 9) Shade
matrix
two dimensional vectors; rectangular objects where all entries have the same type; can be created using cbind( )
$
a shorthand for extracting named elements of list; similar to [ [ ] ] except you don't need to use quotes.
echo=FALSE
option that omits R code but not results
integer vectors
belongs to the numeric class; made by placing an "L" after the number
class( )
a function that returns the classes to which an object belongs to.
comment=NULL
option that places no comment ## in front of output
[ [ ] ]
extracts a single component from a list
error=TRUE
option that knits document even with code error present
Taxonomy for data graphics
1) visual cues 2) coordinate system 3) scale 4) context
c( ) function
concatenates scalars
Section 2
(50 cards)
facet_wrap()
used to facet the plot by a single variable
select( )
takes a subset of the columns specified
filter( )
takes a subset of the rows specified
cartesian coordinate system
the familiar (x, y) rectangular coordinate system with two perpendicular axes
shade
(either) to what extent? how severe?
geom_density( )
creates a density curve in ggplot
key =
the name of the variable in the narrow format that will identify each case individually and receive the values.
ungroup()
returns "focus" back to the entire data frame
coord_quickmap( )
sets the aspect ratio correctly for maps.
categorical scale
may have no ordering (e.g. Democrat, Republican) or be ordinal (Never a Smoker, Current Smoker, Former Smoker)
color= or label=
conveys information about the data by mapping the aesthetics in the plot to the variables in your dataset
draw the figure
draw this figure
geom_histogram( )
creates a histogram in ggplot
group_by()
change the scope, or unit of analysis, from individual cases to aggregated groups
[!is.na()]
omit NAs
semi_join( )
returns all rows from the first table where there are matching values in the second table, keeping just columns from first table.
geographic coordinate system
where we have locations on the curved surface of the earth. Trying to represent these locations on a two dimensional plane.
geom_point( )
adds a layer of points to the ggplot, which creates a scatterplot
interval( )
provides the time elapsed
ylab(" ")
creates a y axis title in ggplot
full_join( )
returns all rows and all columns from both the first table and the second table. Where there are not matching values, returns NA for the one missing. This is a mutating join.
geom_boxplot( )
creates a boxplot in ggplot
layers
adding a new layer on top of an existing data graphic. This new layer can provide context or comparison, but there's a limit to how many layers humans can reliably parse.
lag(x)
shows the time that has passed has passed since x
geom_smooth( )
setting the line type of a line
numeric scale
this quality is most commonly set on a linear, logarithmic, or percentage scale.
color
(either) to what extent? how severe?
coord_flip( )
switches the x and y axes.
spread( )
converts a data table from narrow to wide
polar coordinate system
the radial analog of the cartesian system with points identified by radius p and angle theta
numeric scale
the quality is most commonly set on a linear, logarithmic, or percentage scale
xlab(" ")
creates an x axis title in ggplot
area
(numerical) how big (in two dimensions)?
volume
(numerical) how big (in three dimensions)?
anti_join( )
returns all rows from the first table where there are NOT matching values in the second table, keeping just columns from first table.
context
titles/subtitles; helps the viewer make meaningful comparisons.
geom_polygon()
connects start and end points which fills a closed polygon shape
scale
translates values into visual cues
facets
a single data graphic that can be composed of several small multiples of the same basic plot, with one (discrete) variable changing in each of the small sub-image.
mutate( )
add or modify existing columns
direction
(numerical) at what slope? in a time series, going up or down?
piping %>%
allows you to put the output of one function into the input of another
right_join( )
rows of the second table that are always returned, regardless of whether there's a match in the first table. NAs inserted into columns where no matched data is found.
summarize( )
aggregates data across rows
arrange( )
sorts the rows specified
shape
(categorical) belonging to which group?
geom_path()
connects the dots between x (i.e latitude) and y (i.e. longitude) in a given group
geom_bar( )
adds bars to the ggplot, which creates a bar chart
x1 <- list(c(1, 2), c(3, 4)) x2 <- list(list(1, 2), list(3, 4)) x3 <- list(1, list(2, list(3)))
create the following lists
gather( )
converts a data table from wide to narrow
Section 3
(14 cards)