Week 4: Data Visualisation and Transformation Flashcards
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- Maximise data-to-ink ratio
- Present more data without losing interpretability
- Use levels of detail
What are 3 distilled principles from Tufte?
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geom_point() #scatterplot
geom_density_2d() #contour lines from x and y positions
geom_histogram() #histogram, use binwidth to change size of bins
geom_density() #density plot
geom_rug() #adds rug marks of raw data on the axes
geom_boxplot() #boxplot
geom_bar() #barplot, automatically transforms variables to counts using stat_count
geom_col() #column graph, need x and y variables
geom_line() #line chart
geom_label(aes(x=, y=, label=)) #gives a label at the specified x and y position
geom_freqpoly() #same as histogram but uses lines instead of bars, good for overlapping data
geom_area() #area chart
geom_smooth(method=‘lm’) #draws line of best fit. se=TRUE is default and displays the standard error lines aswell
geom_abline() #adds reference line, default is from data
geom_ribbon(x, ymin, ymax) #draws line with lower and upper bounds e.g. confidence interval
What are some useful geoms? (15)
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filter(!is.na(data))
How do you remove the missing values from a dataframe using filter?
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get the residual and plot the data against the residual
How do you “flatten” a graph?
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more data with less ink on the page
What is a high data-ink ratio?
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ungroup()
How do you remove a grouping to return to operations on ungrouped variables?
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+ xlim(0,5)
+ coord_cartesian(xlim = c( , ))
this way doesn’t throw away the data outside the limits, used to zoom
How do you set axis limits in 2 ways?
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%in% #in
between(x, left, right) #finds rows where x is between left and right
How do you use in and between in R?
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Using aes(group= ) is the same as mapping a variable onto an aesthetic, it separates based on the discrete variable but does not specify the difference with a legend on the graph
What does the “group” mapping do in a geom?
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anything from the input can be called in server using input$…
How do you call something from the input in the server in shiny?
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is.na()
How do you determine if a value is a missing value in R?
# Define a plot called distplot in the server using output$distplot. In ui.R can call directly with distplot
How do you define something e.g. a plot in the server and how do you refer to it in the ui in shiny?
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mutate(data, new column = …)
How do you add a new column to a dataframe?
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nrow =
ncol =
specifies number of rows or columns
What are additional arguments to facet_wrap? (2)
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The output depends on the users input. all output must be wrapped in a renderSomething function, this watches the input and updates accordingly
What is reactivity in Shiny?
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min_rank(x) #gives 1 to the lowest value and so on
min_rank(desc(x)) #gives 1 to the highest value
How do you give a ranking to values in a vector x?
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filter(dataframe, value1==1, value2==4)
How do you select only certain rows of a dataframe based on their values?
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geom_count, creates a graph with different size dots at each intersection
geom_tile with fill aesthetic darker depending on combinations of each value:
data %>% count(variable1, variable2) %>% ggplot(aes(x = variable1, y = variable2)) + geom_tile(aes(fill = n))
What is a good way to display two categorical variables?
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The mapping in the geom overrides the global mapping in ggplot
If you have different mappings in ggplot() and geom(aes()), which one will override?
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read_csv(‘filepath’)
How do you load a csv into a dataframe in R?
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As the number of points and number of categories increases, facet grid becomes better
When should you use facet grid over mapping by colour?
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facet_wrap(~variable)
create formula with ~, variable should be discrete
How do you use facet wrap?
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Facet of 4 graphs with very different data but the same line of best fit, which has the same linear regression coefficient 0.7
What is Ansocombe’s quartet?
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mutate(column = ifelse(test, value1, value2))
test is a logical vector ie column<5
value 1 is what to do when test is true
value 2 is what to do when test is false
How do you replace unusual values with missing values in a dataframe?
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Yes to colour, gives continuous scale. No to shape
Can you map continuous variables to colour and shape?
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cut(variable, breaks=(0,10,20), labels = c(“”, “”))
How do you split a variable into different sections and label the sections?
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+ scale_y_log10() + scale_x_log10()
How do you “straighten” a graph?
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geom_freqploy(aes(x=price, y=..density..))
How do you get a freqpoly to display density instead of count?
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cumsum()
How do you do a cumulative sum?
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E.g. colour = variable <5. Gives true or false for colours
How do you map an aesthetic to a function
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- position on a common scale
- position on an unaligned scale
- length
- tilt/angle
- area
- depth
- colour luminance/colour saturation
- curvature/volume
What is the ranking of effectiveness for ordered attributes? (8)
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data %>% group_by(variable) %>% summarise(newname = mean(distance, na.rm=TRUE))
How do you get a grouped summary (mean for this question) of a variable grouped by another variable?
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- Unhelpful errors
- Dependency hell
- Unreliable back end
- Need to run R on a server
- Reactivity can be slow
What are the disadvantages of r shiny? (5)
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sum(x>10) gives the number of TRUE’s in x>10
mean(x>10) gives the proportion of TRUEs in x>10
How do you get a count of how many x>10 in a variable? How do you get a proportion?
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arrange(data, desc(column1))
How do you arrange rows in descending order?
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library(tidyverse)
What package is ggplot2 in?
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mean ()
sd()
How do you get mean and standard deviation?
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colour = NA
How do you change the colour to no colour?
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contains everything which should be done in the background
What is contained in the server.R file in shiny?
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Put the variable with more levels in the columns
Using facet grid, which variable should you put in the rows and which in the columns?
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arrange(data, column1, column2) #orders by column 1 then column 2 in ascending order
How do you change the order of rows?
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Excludes them automatically
What does filter do with NA values?
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- electric shock
- saturation
- length
- area
- depth
- brightness
What is the order of how humans perceive sensations? (6)
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Gives NA when there are missing values
Use na.rm=TRUE to remove missing values prior to calculation
What do aggregate functions do when there are missing values? How do you change the default?
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transmute(data, newcolumn = …)
How do you add a new column to a dataframe and keep only the new columns?
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geom_point (scatterplot)
geom_bin2d and geom_hex() divide plane into 2d bins and use to colour to display how many points in each bin
use boxplot and divide one continuous variable into a categorical: geom_boxplot(aes(group = cut_width(x, width))
What is a good way to display two continuous variables? (3)
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library(GGally)
ggpairs(data, columns= c(‘column1’, ‘column2’, ‘column3’)]
What is a different way of creating a matrix of plots?
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- spatial region
- colour hue
- motion
- shape
What is the ranking of effectiveness for categorical attributes? (4)
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provides schematic for how the application will be presented to the user. e.g. titlePanel(), sidebarLayout(), sidebarPanel(), mainPanel()
What is contained in the ui.R file in shiny?
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, >=, !=, ==
What are the comparison operators in R?
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If it gives information about a variable it goes inside the aes(). If not it must go outside the aes()
Does the aesthetic mapping go inside or outside the aes()?
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tibble(column1= , column2= )
data.frame(column1=, column2= )
can use as.character(column1= )
data.frame automatically sets characters as factors unless you set stringsAsFactors=FALSE
What are 2 codes to make vectors into a dataframe?
How do you specify the type?
What is a difference between the 2 codes?
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Facets are subplots that each display a subset of the data
What is a facet?
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- Aesthetics (position, shape, colour, …)
- Geometric objects (points, lines, bars, …)
- Scales (continuous, discrete, Cartesian coordinates, …)
- Facets (small multiples)
- Statistical transformation (identity, binning, median, …)
- Coordinate system (Cartesian, polar, parallel, …)
What are the layers of Wickhams grammar of graphics? (6)
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Like a boxplot but shows the full density plots
What is a violin plot?
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!!vector #bang-bang operator, matches to names of variables in vector
all_of(vector)
any_of(vector)
#in all of, all names must be present. in any of they don’t
How do you select columns by matching them to names contained in a string vector? (3 ways)
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- Additional groups will go unplotted
How many shapes can you plot as a mapping? What happens if there are more than that many factors?
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+ labs(y= “”, x= “”)
How do you label the axes?
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geom_point(position=“jitter”) OR geom_jitter()
What are two ways to add jitter to a plot?
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- Proximity: things that are spatially near to one another seem to be related
- Similarity: things that look alike seem to be related
- Connection: things that are visually tied to one another seem to be related
- Continuity: partially hidden objects are completed into familiar shapes
- Closure: incomplete shapes are perceived as complete
- Figure and ground: visual elements are taken to be either in the foreground or in the background
- Common fate: elements sharing a direction of movement are perceived as a unit
What are the Gestalt principles of relatedness? (7)
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& #and
| #or
! #not
What are the logical operators in R?
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coord_cartesian() #default
coord_flip() #switches the x and y axis
coord_map() #sets the aspect ratio correctly for maps
coord_quickmap() #sets the aspect ratio correctly for maps, quicker
coord_polar() #uses polar coordinates. use argument (theta=“y”) to create a pie chart. otherwise you get a bulls-eye chart
coord_fixed() #forces a specified ratio between the axes, default is 1
What are 6 coordinate systems in ggplot?
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boxplot
freqpoly, map by colour
What is a good way to display a categorical variable vs a continuous variable?
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count(variable1, variable2)
gives number of combinations in a table
How do you get the counts of each combination when comparing 2 categorical variables?
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ui
What is the structure of a shiny app?
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How humans perceive sensations compared to how they actually change
What is Steven’s Psychophysical Power Law?
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Can’t be at the beginning of a line. Must be at end of previous line
When using the + in ggplot, where in the line must it go?
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data[1:200,]
code to keep the first 200 rows and all columns of a dataframe?
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ggplot(data = ) +
geom(mapping=aes(), stat=, position=) +
+
What is the general format of a ggplot code?
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rename(data, newname = variable1)
How do you rename a variable?
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show.legend = FALSE
How do you remove the legend?
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Uses statistical transformation stat_count() to find the count of each variable. Can override using stat = “identity” for example to use a y value instead of count
How does geom_bar get the count for each variable? How do you override it?
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facet_grid(variable1~variable2)
How do you facet a plot on a combination of 2 variables?
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ggplot(data) + geom_boxplot(aes(x = reorder(xvariable, yvariable, FUN = median), y = yvariable))
How do you reorder boxplots by median?
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geom_bar creates is own bin for NAs
geom_histogram removes missing values
What happens to missing values in geom_bar and geom_histogram?
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max(variable) #gives max value
which.max(variable) #gives location of max value
How do you get the max value of a variable and the location of the max value?
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bar chart
What is a good way to visualise a single categorical variable?
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select(data, variable1, variable2)
How do you select only certain columns of a dataframe?
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The bars are automatically stacked with colours for each object in the variable (position = “stack”)
position = “identity” #places each object exactly where it falls in context of graph. Will include overlapping so should use alpha position = “fill” #works like stacking but makes each set of stacked bars the same height. Makes it easier to compare proportions across groups position = “dodge” #places overlapping objects beside each other. Makes it easier to compare individual values
What happens when you map an aesthetic (colour) to a bar chart? What 3 ways are there to change how this looks?
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lead(x) removes first number and adds NA to end
lag(x) adds NA to beginning and removes last number
What do lead(x) and lag(x) do to a vector x?
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select(data, variable5, variable7, everything()) #moves variables 5 and 7 to the start but still keeps all others
How do you rearrange the columns to put certain columns at the start?
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colour #changes colour,
size #changes size
alpha #changes transparency between 0 and 1
shape #changes shape
linetype #from 0-6. 0 is blank, 1 is solid, others are dotted or dashed
fill #fill colour of shape or curve
stroke #modify width of border. E.g. on shapes
fontface #character “plain”, “bold”, “italic” “bold.italic”
group #groups by a specified variable
What are some possible aesthetic mappings? (9)
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histogram, puts continuous variables into bins density plot (smoothed histogram)
What is a good way to visualise a single continuous variable? (2)
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select(data, -(variable1))
How do you exclude a column from a dataframe?
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%/% (integer division)
%% (remainder)
What are the modular arithmetic symbols?
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table(variable)
How do you create a table with a count for each value in a variable?
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starts_with(“abc”) c
ends_with(“abc”)
contains(“abc”)
matches(“expression”)
How do you select column that start, with, end with, contain or match a string?
