Note: This document was converted to R-Markdown from this page, with modifications, by M. Drew LaMar. You can download the R-Markdown here.

Download the R code on this page as a single file here

New methods

Hover over a function argument for a short description of its meaning. The variable names are plucked from the examples further below.

Read data from a comma-separated (.csv) file into a data frame. R will take columns having only numbers and make them numeric variables in the data frame. Columns having characters will be converted to factor variables, rather than to character variables.

locustData <- read.csv(chap02f1_2locustSerotonin.csv)

Inspect data in a data frame. The head function shows the first few lines of the data frame to confirm the data was read properly. The nrow function indicates the number of cases (rows) in the data frame.

head(locustData)
nrow(locustData)

Basic strip chart relating a numeric variable to a categorical variable:

stripchart(serotoninLevel ~ treatmentTime, data = locustData, method = “jitter”, vertical = TRUE)

Frequency table or contingency table:

table(tigerData$activity)

Bar graph for count data:

barplot(tigerTable, ylab = “Frequency”, cex.names = 0.5)

Histogram for a numeric variable:

hist(birdAbundanceData$abundance, right = FALSE)

Scatter plot showing association between two numeric variables:

plot(sonAttractiveness ~ fatherOrnamentation, data = guppyFatherSonData)

Other new methods:

Plotting cheatsheet

These tables were created by M. Drew LaMar, based on ones at the end of Chapter 2 of Whitlock & Schluter’s textbook.

Frequency distributions of univariate data

Type of data Graphical method R command Example
Categorical Bar graph barplot Figure 2.1-3. Education spending (processed)
“ “ “ Example 2.2A. Deaths from tigers (raw)
Numerical Histogram hist Figure 2.2-5. Salmon body size

Showing association of bivariate data

Type of data Graphical method R command Example
Two numerical Scatter plot plot Example 2.3B. Guppy father and son comparison
“ Line plot plot Example 2.4A. Measles outbreaks
“ Map — —
Two categorical Grouped bar graph barplot Example 2.3A. Bird malaria
“ Mosaic plot mosaicplot Example 2.3A. Bird malaria
Mixed Strip chart stripchart Example 2.3C. Human hemoglobin and elevation
“ Box plot boxplot Example 2.3C. Human hemoglobin and elevation
“ Multiple histograms hist Example 2.3C. Human hemoglobin and elevation
“ Cumulative frequency distributions — —

Figure 2.1-2. Locust serotonin

Strip chart of serotonin levels in the central nervous system of desert locusts that were experimentally crowded for 0 (the control group), 1, and 2 hours.

Read the data and store in data frame (here named locustData). The following command uses read.csv to grab the data from a file on the internet (on the current web site).

locustData <- read.csv("http://whitlockschluter.zoology.ubc.ca/wp-content/data/chapter02/chap02f1_2locustSerotonin.csv")

Show the first few lines of the data, to ensure it read correctly. Determine the number of cases in the data.

head(locustData)
##   serotoninLevel treatmentTime
## 1            5.3             0
## 2            4.6             0
## 3            4.5             0
## 4            4.3             0
## 5            4.2             0
## 6            3.6             0
nrow(locustData)
## [1] 30

Draw a stripchart (the tilde “~” means that the first argument below is a formula, relating one variable to the other).

stripchart(serotoninLevel ~ treatmentTime, 
           data = locustData, 
           method = "jitter", 
           vertical = TRUE)

A fancier strip chart, closer to that shown in Figure 2.1-2, by including more options.

# Stripchart with options
par(bty = "l") # plot x and y axes only, not a complete box
stripchart(serotoninLevel ~ treatmentTime, 
           data = locustData, 
           vertical = TRUE, 
           method = "jitter", 
           pch = 16, 
           col = "firebrick", 
           cex = 1.5, 
           las = 1,
           ylab = "Serotonin (pmoles)", 
           xlab = "Treatment time (hours)",
           ylim = c(0, max(locustData$serotoninLevel)))

# The following command calculates the means in each treatment group (time)
meanSerotonin = tapply(locustData$serotoninLevel, 
                       locustData$treatmentTime, 
                       mean)
# "segments" draws draws lines to indicate the means
segments(x0 = c(1,2,3) - 0.1, 
         y0 = meanSerotonin, 
         x1 = c(1,2,3) + 0.1, 
         y1 = meanSerotonin, lwd = 2)

Figure 2.1-3. Education spending

A bar graph of education spending per student in different years in British Columbia.

Read the data into a data frame named educationSpending, and inspect.

educationSpending <- read.csv("http://whitlockschluter.zoology.ubc.ca/wp-content/data/chapter02/chap02f1_3EducationSpending.csv")
head(educationSpending)
##   year spendingPerStudent
## 1 1998               5844
## 2 1999               5983
## 3 2000               6216
## 4 2001               6328
## 5 2002               6455
## 6 2003               6529

Draw a bar graph. The names argument generates numbers between 1998 and 2004 in 1-year increments, to be used as labels along the horizontal axis.

barplot(educationSpending$spendingPerStudent, 
        names.arg = educationSpending$year,
        ylab = "Education spending ($ per student)")

A slightly fancier bar graph like that in Figure 2.1-3, which includes additional options, is shown here.

# Bar graph with more options
barplot(educationSpending$spendingPerStudent, 
        names.arg = educationSpending$year, 
        las = 1, 
        col = "firebrick", 
        ylim = c(0,8000),
        ylab = "Education spending ($ per student)")

Example 2.2A. Deaths from tigers

Frequency table and bar graph showing activities of 88 people at the time they were killed by tigers near Chitwan National Park, Nepal, from 1979 to 2006.

Read the data into data frame named tigerData

tigerData <- read.csv("http://whitlockschluter.zoology.ubc.ca/wp-content/data/chapter02/chap02e2aDeathsFromTigers.csv")
head(tigerData)
##   person              activity
## 1      1 Disturbing tiger kill
## 2      2       Forest products
## 3      3          Grass/fodder
## 4      4       Fuelwood/timber
## 5      5          Grass/fodder
## 6      6       Forest products

Generate a frequency table. The sort function is included to sort the categories by their frequencies.

tigerTable <- sort(table(tigerData$activity), decreasing = TRUE)
tigerTable
## 
##          Grass/fodder       Forest products               Fishing 
##                    44                    11                     8 
##               Herding Disturbing tiger kill       Fuelwood/timber 
##                     7                     5                     5 
##     Sleeping in house               Walking                Toilet 
##                     3                     3                     2

You can arrange the frequency table vertically.

data.frame(Frequency = tigerTable)
##          Frequency.Var1 Frequency.Freq
## 1          Grass/fodder             44
## 2       Forest products             11
## 3               Fishing              8
## 4               Herding              7
## 5 Disturbing tiger kill              5
## 6       Fuelwood/timber              5
## 7     Sleeping in house              3
## 8               Walking              3
## 9                Toilet              2

Use the addmargins command to include sums in your frequency table.

data.frame(Frequency = addmargins(tigerTable))
##           Frequency.Var1 Frequency.Freq
## 1           Grass/fodder             44
## 2        Forest products             11
## 3                Fishing              8
## 4                Herding              7
## 5  Disturbing tiger kill              5
## 6        Fuelwood/timber              5
## 7      Sleeping in house              3
## 8                Walking              3
## 9                 Toilet              2
## 10                   Sum             88

Draw a bar graph. The additional arguments cex.names = 0.5 shrinks the axis labels by 50%, and las = 2 flips the labels, so that they all fit in the window.

barplot(tigerTable, 
        ylab = "Frequency", 
        cex.names = 0.5, 
        las = 2)

A slightly fancier bar graph of the data with more options, like that shown in Figure 2.2-1, is shown here.

oldpar = par(no.readonly = TRUE) # stores a backup copy of current graph settings in "oldpar"
par(mar = c(8, 4, 4, 2) + 0.1)   # creates more room for labels below the x-axis
barplot(tigerTable, 
        las = 2, 
        col = "firebrick", 
        cex.names = 0.8, 
        ylim = c(0,50), 
        xlab = "", 
        ylab = "Frequency (number of people)")
mtext("Activity", 
      side = 1, 
      line = 7, 
      cex = 0.9) # adds the text under the x-axis

par(oldpar)  # reverts graph settings back to default

Example 2.2B. Desert bird abundance

Frequency table and histogram illustrating the frequency distribution of bird species abundance at Organ Pipe Cactus National Monument.

Read and inspect the data.

birdAbundanceData <- read.csv("http://whitlockschluter.zoology.ubc.ca/wp-content/data/chapter02/chap02e2bDesertBirdAbundance.csv")
head(birdAbundanceData)
##            species abundance
## 1    Black Vulture        64
## 2   Turkey Vulture        23
## 3    Harris's Hawk         3
## 4  Red-tailed Hawk        16
## 5 American Kestrel         7
## 6   Gambel's Quail       148

Generate a frequency table of the numeric bird abundance variable. The option right = FALSE ensures that abundance value 300 (for example) is counted in the 300-400 bin rather than in the 200-300 bin.

birdAbundanceTable <- table(cut(birdAbundanceData$abundance, 
                                breaks = seq(0,650,by=50), 
                                right = FALSE))
birdAbundanceTable
## 
##    [0,50)  [50,100) [100,150) [150,200) [200,250) [250,300) [300,350) 
##        28         4         3         3         1         2         1 
## [350,400) [400,450) [450,500) [500,550) [550,600) [600,650) 
##         0         0         0         0         0         1

The same table oriented vertically and including the sum.

data.frame(Frequency = addmargins(birdAbundanceTable))
##    Frequency.Var1 Frequency.Freq
## 1          [0,50)             28
## 2        [50,100)              4
## 3       [100,150)              3
## 4       [150,200)              3
## 5       [200,250)              1
## 6       [250,300)              2
## 7       [300,350)              1
## 8       [350,400)              0
## 9       [400,450)              0
## 10      [450,500)              0
## 11      [500,550)              0
## 12      [550,600)              0
## 13      [600,650)              1
## 14            Sum             43

Draw a histogram of bird abundances.

hist(birdAbundanceData$abundance, right = FALSE)

Commands to draw a histogram with more options, such as Figure 2.2-3, are here.

# Histogram with options
hist(birdAbundanceData$abundance, 
     right = FALSE, 
     breaks = seq(0,650,by=50), 
     col = "firebrick", 
     las = 1, 
     xlab = "Abundance (No. individuals)",  
     ylab = "Frequency (No. species)", main = "")

Figure 2.2-5. Salmon body size

Histograms of body mass of 228 female sockeye salmon sampled from Pick Creek in Alaska. The same data are plotted for three different interval widths: 0.1 kg, 0.3 kg, and 0.5 kg.

Read the data into data frame named salmonSizeData

salmonSizeData <- read.csv("http://whitlockschluter.zoology.ubc.ca/wp-content/data/chapter02/chap02f2_5SalmonBodySize.csv")
head(salmonSizeData)
##   year   sex oceanAgeYears lengthMm massKg
## 1 1996 FALSE             3      513  3.090
## 2 1996 FALSE             3      513  2.909
## 3 1996 FALSE             3      525  3.056
## 4 1996 FALSE             3      501  2.690
## 5 1996 FALSE             3      513  2.876
## 6 1996 FALSE             3      501  2.978

Histograms with different bin widths (0.1, 0.3, and 0.5).

hist(salmonSizeData$massKg, 
     right = FALSE, 
     breaks = seq(1,4,by=0.1), 
     col = "firebrick")

hist(salmonSizeData$massKg, 
     right = FALSE, 
     breaks = seq(1,4,by=0.3), 
     col = "firebrick")

hist(salmonSizeData$massKg, 
     right = FALSE, 
     breaks = seq(1,4,by=0.5), 
     col = "firebrick")

Example 2.3A. Bird malaria

Contingency table, grouped bar plot, and mosaic plot showing the association between egg removal treatment and incidence of malaria in female great tits.

Read the data from the data file and inspect.

birdMalariaData <- read.csv("http://whitlockschluter.zoology.ubc.ca/wp-content/data/chapter02/chap02e3aBirdMalaria.csv")
head(birdMalariaData)
##   bird treatment response
## 1    1   Control  Malaria
## 2    2   Control  Malaria
## 3    3   Control  Malaria
## 4    4   Control  Malaria
## 5    5   Control  Malaria
## 6    6   Control  Malaria

Optional step: Set the desired order of treatment categories in tables and graphs. The factor command allows us to order the levels so that the category “Egg removal” comes before “Control” in tables and graphs (categories are otherwise ordered alphabetically).

birdMalariaData$treatment <- factor(birdMalariaData$treatment, levels= c("Egg removal", "Control"))

Create a contingency table. Use table with the names of two categorical variables as arguments, beginning with the response variable.

birdMalariaTable <- table(birdMalariaData$response, birdMalariaData$treatment)
birdMalariaTable
##             
##              Egg removal Control
##   Malaria             15       7
##   No Malaria          15      28

Include row and column sums in the contingency table.

addmargins(birdMalariaTable, 
           margin = c(1,2), 
           FUN = sum, 
           quiet = TRUE)
##             
##              Egg removal Control sum
##   Malaria             15       7  22
##   No Malaria          15      28  43
##   sum                 30      35  65

Draw a grouped bar graph using the contingency table.

barplot(as.matrix(birdMalariaTable), beside = TRUE)

Commands to produce a grouped bar graph with more options are shown here.

# Grouped bar graph with options
barplot(as.matrix(birdMalariaTable), 
        beside = TRUE, 
        space = c(0.1, 0.3),
        las = 1, 
        xlab = "Treatment", 
        ylab = "Relative frequency",
        col = c("firebrick", "goldenrod1"), 
        legend.text = rownames(birdMalariaTable), 
        args.legend = list(x = 0.3,
                           y = max(birdMalariaTable), 
                           xjust = 0))

Draw a mosaic plot. The “t” command flips (transposes) the table to ensure that the explanatory variable is along the horizontal axis.

mosaicplot(t(birdMalariaTable), 
           col = c("firebrick", "goldenrod1"), 
           sub = "Treatment", 
           ylab = "Relative frequency", 
           cex.axis = 1.1, 
           main = "")

Example 2.3B. Guppy father and son comparison

Scatter plot of the relationship between the ornamentation of male guppies and the average attractiveness of their sons.

Read the data from the file.

guppyFatherSonData <- read.csv("http://whitlockschluter.zoology.ubc.ca/wp-content/data/chapter02/chap02e3bGuppyFatherSonAttractiveness.csv")
head(guppyFatherSonData)
##   fatherOrnamentation sonAttractiveness
## 1                0.35             -0.32
## 2                0.03             -0.03
## 3                0.14              0.11
## 4                0.10              0.28
## 5                0.22              0.31
## 6                0.23              0.18

Draw a scatter plot using the formula approach (with the “~”).

plot(sonAttractiveness ~ fatherOrnamentation, data = guppyFatherSonData)

See here for commands to draw a fancier scatter plot like that in Figure 2.3-3.

# Scatter plot with options
plot(sonAttractiveness ~ fatherOrnamentation, 
     data = guppyFatherSonData, 
     las = 1, 
     pch = 16, 
     col = "firebrick", 
     cex = 1.5, 
     bty = "l", 
     xlab = "Father's ornamentation", 
     ylab = "Son's attractiveness")

Example 2.3C. Human hemoglobin and elevation

Strip chart, box plot, and multiple histograms showing hemoglobin concentration in men living at high altitude in three different parts of the world and in a sea level population (USA).

Read the data.

hemoglobinData <- read.csv("http://whitlockschluter.zoology.ubc.ca/wp-content/data/chapter02/chap02e3cHumanHemoglobinElevation.csv")
head(hemoglobinData)
##              id hemoglobin population
## 1 US.Sea.level1      10.40        USA
## 2 US.Sea.level2      11.20        USA
## 3 US.Sea.level3      11.70        USA
## 4 US.Sea.level4      11.80        USA
## 5 US.Sea.level5      11.90        USA
## 6 US.Sea.level6      12.05        USA

Obtain the sample sizes in each of the four populations

table(hemoglobinData$population)
## 
##    Andes Ethiopia    Tibet      USA 
##       71      128       59     1704

Draw a strip chart of the hemoglobin data.

stripchart(hemoglobin ~ population, 
           data = hemoglobinData, 
           method = "jitter",
           vertical = TRUE)

Commands for a fancier strip chart like that shown in Figure 2.3-4 are here.

par(bty = "l")
stripchart(hemoglobin ~ population, 
           data = hemoglobinData, 
           vertical = TRUE, 
           method = "jitter", 
           jitter = 0.2, 
           pch = 1, 
           col = "firebrick",
           las = 1, 
           xlab = "Male population", 
           ylab = "Hemoglobin concentration (g/dL)")

Draw a box plot, relating hemoglobin to population.

boxplot(hemoglobin ~ population, data = hemoglobinData)

A box plot with more options, like that in Figure 2.3-4, is shown here.

par(bty = "l")
boxplot(hemoglobin ~ population, 
        data = hemoglobinData,
        col = "goldenrod1", 
        boxwex = 0.5, 
        whisklty = 1, 
        outcol = "black", 
        outcex = 1, 
        outlty = "blank", 
        las = 1, 
        xlab="Male population", 
        ylab = "Hemoglobin concentration (g/dL)")

Show the association between hemoglobin and population using the multiple histograms approach (Figure 2.3-5). The following commands use the lattice package, which must first be loaded.

library(lattice)
histogram(~ hemoglobin | population, 
          data = hemoglobinData,
          layout = c(1,4), 
          col = "firebrick", 
          breaks = seq(10,26,by=1))

Here we show commands to draw the multiple histograms in basic R, without using the lattice package. This approach is more tedious, but the resulting graphs are often easier to modify.

# Multiple histograms using base graphics, plotting them one at a time.
# The "oma" option adjusts the outer margins of the whole figure
# The "mar" option tweaks the margins within each of the 4 plots.
oldpar = par(no.readonly = TRUE) # make backup of default graph settings
par(mfrow = c(4,1), 
    oma = c(4, 6, 2, 6), 
    mar = c(2, 5, 4, 2))

hist(hemoglobinData$hemoglobin[hemoglobinData$population == "Andes"],
     col = "firebrick", 
     las = 1, 
     main = "Andes",  
     breaks = seq(10,26,by=1), 
     ylab = "Frequency")

hist(hemoglobinData$hemoglobin[hemoglobinData$population == "Ethiopia"],
     col = "firebrick", 
     las = 1, 
     main = "Ethiopia",  
     breaks = seq(10,26,by=1), 
     ylab = "Frequency")

hist(hemoglobinData$hemoglobin[hemoglobinData$population == "Tibet"],
     col = "firebrick", 
     las = 1, 
     main = "Tibet",  
     breaks = seq(10,26,by=1), 
     ylab = "Frequency")

hist(hemoglobinData$hemoglobin[hemoglobinData$population == "USA"],
     col = "firebrick", 
     las = 1, 
     main = "USA",  
     breaks = seq(10,26,by=1), 
     ylab = "Frequency")

mtext("Hemoglobin concentration (g/dL)", 
      side = 1, 
      outer = TRUE, 
      padj = 1.5)

par(oldpar) # revert to default graph settings

Example 2.4A. Measles outbreaks

Line graph showing confirmed cases of measles in England and Wales from 1995 to 2011. Annual counts are quarterly.

Read the data from file.

measlesData <- read.csv("http://whitlockschluter.zoology.ubc.ca/wp-content/data/chapter02/chap02e4aMeaslesOutbreaks.csv")
head(measlesData)
##   year quarter confirmedCases yearByQuarter
## 1 2011     4th            136       2011.88
## 2 2011     3rd            154       2011.62
## 3 2011     2nd            346       2011.38
## 4 2011     1st            151       2011.12
## 5 2010     4th             31       2010.88
## 6 2010     3rd            134       2010.62

Drawing a line graph uses the same command as a scatter plot but adds the type = "l" argument to draw a line graph instead.

plot(confirmedCases ~ yearByQuarter, 
     data = measlesData, 
     type="l")

Commands to draw a fancier line plot (like that in Figure 2.4-1) are shown here.

# Line plot with options
plot(confirmedCases ~ yearByQuarter, 
     data = measlesData, 
     type = "l", 
     las = 1, 
     lwd = 1, 
     bty = "l",
     xlab = "Year",
     ylab = "Number of cases", 
     xaxp = c(1995,2012,2012-1995))

points(confirmedCases ~ yearByQuarter, 
       data = measlesData, 
       pch = 16, 
       col = "firebrick", 
       cex = 0.7)