R Plot - Function Curve Chart

Function curve graphs are an important tool for studying functions.

The curve() function in R can draw the image of a function, and the code format is as follows:

curve(expr, from = NULL, to = NULL, n =　101, add = FALSE,
　　　　　　type = "l", xname = "x", xlab = xname, ylab = NULL,
　　　　　　log = NULL, xlim = NULL, ...)
# S3　function methods
plot(x, y = 0, to =　1, from = y, xlim = NULL, ylab = NULL, ...)

Note:R language classes have S3 class and S4 class, S3 The class is widely used, creating simple and rough but flexible, while S4 The class is relatively refined.

Parameters:

• expr: the function expression.

• from and to: the start and end range of the plot.

• n: an integer value representing the number of values x takes.

• add: a logical value, indicating that the plot is added to an existing plot when TRUE.

• type: the type of plotting, p for point, l for line, o to draw both points and lines, with the line passing through the points.

• xname: the name used for the x-axis variable.

• xlim and ylim represent the range of the x-axis and y-axis.

• xlab, ylab: the label names of the x-axis and y-axis.

In the plot function, x and y represent the abscissa and ordinate of the drawn figure, respectively.

Here we draw a chart of the sin(x) function:

curve(sin(x))　-2　*　pi,　2　*　)pi

Note: Any computer drawing tool draws pattern charts, which cannot guarantee that they are exactly the same as the true function images. It only takes a point at a certain distance, then calculates the "height" of this point and draws it out. To ensure the continuity of the curve, there will be a straight line connecting adjacent points, so in some cases such as tan(x), errors may occur:

at each (2n+1)Pi / 2 locations will appear breakpoints, but R's images connect them, I hope everyone understands this point.

Of course, not all functions support vector processing like sin, we can also manually generate a number sequence and then use the plot function to generate a function image. Assuming the function f only supports a single number as a parameter:

# Define function f
f = function(x) {
　　　　if (x >= 0) {
　　　　　　　　x
　　　　} else {
　　　　　　　　x ^　2
　　　　}
}
# Generate independent variable sequence
x = seq(-2,　2, length=100)
# Generate dependent variable sequence
y = rep(0, length(x))
j =　1
for (i in x) {
　　　　y[j] = f(i)
　　　　j = j　+　1
}
# Draw the image
plot(x, y, type='l')

Next, we use the plot() function to plot vector data:

# Vector data
v <-　c(7,12,28,3,41)
# Generate image
png(file = "line_chart_label_colored.jpg")
# Plotting, line chart color is red, the main parameter is used to set the title
plot(v, type = "o", col = "red", xlab = "Month", ylab = "Rain fall"
　　　main = "Rain fall chart"