To further explore line charts, we will experiment with modifying line widths and adding multiple custom lines to our graphics:
- Use the
lwdargument to set the line width:> #modify the chapter 8 single line chart that depicted the durations of past fire attacks > #use the lwd argument to set the line width > #lwd accepts a nonnegative value and defaults to 1 > lineFireDurationWidth <- 3 > #use plot(...) to create and display the line chart > #recall that a line chart uses the same plot(...) function as a scatterplot, but with a different type argument > plot(x = lineFireDurationDataX, y = lineFireDurationDataY, main = lineFireDurationMain, xlab = lineFireDurationLabX, ylab = lineFireDurationLabY, type = lineFireDurationType, lwd = lineFireDurationWidth)
- Your chart will be displayed in the graphic window, as shown in the following:
- Prepare the line chart to incorporate additional data:
> #prepare the line chart to incorporate data from the other battle methods > #modify the chart title > lineFireDurationMain = "Duration by Battle Method" > #rescale the y axis to handle the new data > lineFireDurationLimY <- c(0, 200) > #incorporate the col argument to distinguish between the different battle methods > lineFireDurationCol <- "red" > #use plot(...) to create and display the line chart > plot(x = lineFireDurationDataX, y = lineFireDurationDataY, main = lineFireDurationMain, xlab = lineFireDurationLabX, ylab = lineFireDurationLabY, ylim = lineFireDurationLimY, type = lineFireDurationType, lwd = lineFireDurationWidth, col = lineFireDurationCol)
- Your chart will be displayed in the graphic window as shown:
- Use the
lines(...)function to add new relationships to the line chart:> #use lines(...) to add new relationships to a line chart > #add lines representing the three remaining battle methods to the chart > #note that after entering each subsequent function into the R console, it will be immediately drawn atop your existing line chart > #ambush > lineAmbushDataY <- subsetAmbush$DurationInDays > lineAmbushWidth <- 1 > lineAmbushCol <- "blue" > lines(x = lineFireDurationDataX, y = lineAmbushDataY, type = lineFireDurationType, lwd = lineAmbushWidth, col = lineAmbushCol) > #head to head > lineHeadToHeadDataY <- subsetHeadToHead$DurationInDays > lineHeadToHeadWidth <- 1 > lineHeadToHeadCol <- "darkorange2" > lines(x = lineFireDurationDataX, y = lineHeadToHeadDataY, type = lineFireDurationType, lwd = lineHeadToHeadWidth, col = lineHeadToHeadCol) > #surround > lineSurroundDataY <- subsetSurround$DurationInDays > lineSurroundWidth <- 1 > lineSurroundCol <- "forestgreen" > lines(x = lineFireDurationDataX, y = lineSurroundDataY, type = lineFireDurationType, lwd = lineSurroundWidth, col = lineSurroundCol)
- Your lines will be added to the existing chart, as shown in the following:
- Add a legend to the chart in the following way:
> #add a legend to our line chart > #use the x and y arguments to specify the exact location of the legend > #add labels for the battle methods > #add fill colors to match the chart's lines > legend(x = 23, y = 210, legend = c("Fire", "Ambush", "Head to Head", "Surround"), fill = c("red", "blue", "darkorange2", "forestgreen")) - Your legend will be added to the existing chart; the final chart looks like the following:
We expanded our use of the plot(...) function to generate a line chart with a specific line width. Then, we worked to add additional lines to our chart for the purpose of portraying multiple relationships. We also incorporated a legend to make our chart more legible. Let us review these techniques.
We specified the width of our chart's line using the lwd argument. This argument has a default value of 1 and can receive any number greater than zero. In most cases, you will want to use values between 1 and 3. Both our one-line and multiline charts used a lwd value of 3 to emphasize the fire attack duration data by thickening its line.
> lineFireDurationWidth <- 3
The lwd argument was seamlessly integrated into our plot(...) function:
> plot(x = lineFireDurationDataX, y = lineFireDurationDataY, main = lineFireDurationMain, xlab = lineFireDurationLabX, ylab = lineFireDurationLabY, type = lineFireDurationType, lwd = lineFireDurationWidth)
Note
Note that the lwd argument can be used to modify the line thickness of data markers. For example, using a lwd of 3 in a scatterplot would yield points with thicker markers. The lwd argument can also be used within the abline(...) function to alter a best fit line.
To add new relationships to our multiline chart, we employed the lines(...) function. This function is used to draw additional lines on the chart that is displayed in the graphic window. The primary arguments of the lines(...) function are:
Thus, the general format for the lines(...) function is as follows:
lines(x = xPosition, y = yPosition, type = "type", col = "colorName")
After generating our chart with only fire attack data, we used lines(...) to graph the duration values for our ambush, head to head, and surround methods. For these lines, we used a more subtle lwd value of 1 and custom colors to differentiate them from one another.
> #ambush lines(...) functionexample> lineAmbushWidth <- 1 > lineAmbushCol <- "blue" > #head to head > lineHeadToHeadWidth <- 1 > lineHeadToHeadCol <- "darkorange2" > #surround > lineSurroundWidth <- 1 > lineSurroundCol <- "forestgreen"
A unique line(...) function for battle method was executed to add its data to the line chart:
> #ambush > lines(x = lineFireDurationDataX, y = lineAmbushDataY, type = lineFireDurationType, lwd = lineAmbushWidth, col = lineAmbushCol) > #head to head > lines(x = lineFireDurationDataX, y = lineHeadToHeadDataY, type = lineFireDurationType, lwd = lineHeadToHeadWidth, col = lineHeadToHeadCol) > #surround > lines(x = lineFireDurationDataX, y = lineSurroundDataY, type = lineFireDurationType, lwd = lineSurroundWidth, col = lineSurroundCol)
Note
Note that we also redefined the y-axis scale with ylim prior to adding our new lines. This is necessary, because it allows all of our values to display within the bounds of our chart. If we did not rescale the y-axis, most of our points would fall outside the upper limit of our graph. This is because the fire attack duration values are much smaller than in our other battle methods.
When adding new relationships to a graphic, remember to adjust your axes accordingly to ensure that all data are represented.
Once again, we added a legend to our chart in order to identify each line. We used the already familiar legend(...) function to do so, making sure to match the legend's title and colors to those of the lines on our chart:
> legend(x = 23, y = 210, legend = c("Fire", "Ambush",
"Head to Head", "Surround"), fill = c("red", "blue", "darkorange2",
"forestgreen"))
- In the
plot(...)function, which of the following is not true of thelwdargument?a. One or more of a chart's lines can have a unique
lwdvalue.b. The
lwdargument defaults to a value of 1.c. The
lwdargument accepts a nonnegative numeric value.d. To take effect, the
ltyargument must be defined. - When using the
lines(...)function to add new lines to a chart, which of the following is not a true statement?a. One or more lines can be added to a single chart.
b. The widths of a chart's lines can be different.
c. To display a new line, the chart's data must be in matrix form.
d. The x or y axis may need to be rescaled to properly portray a new line.
Create a multiline chart that portrays the number of Shu soldiers engaged in all instances of each battle method. You should have a line for each battle method. Be sure to experiment with the type and lwd arguments, as well as the lines(...) function, to witness the different line chart styles that can be generated in R. Once your graph is complete, remember to add a legend that identifies each line.