Program 1 , “ Histogram ,” takes an integer “n,” and two integers “left and righ
ID: 3750700 • Letter: P
Question
Program 1, “Histogram,” takes an integer “n,” and two integers “left and right,” and uses “StdDraw” to plot a histogram of the count of the numbers in the standard input stream that fall in each of the n intervals defined by dividing (left, right) into n equal-sized intervals.
Note: The program is to read the values from an input file whose first line would contain “n,” “left,” and “right” values. The remaining lines would contain the sequence of integer values.
A sample run would be as follows.
>more data.txt
4 40 80
52 41 72 61
71 60 50 52 61
77 41 61 70 79 41
67 60 50 61 76
>java Histogram < data.txt
It should plot a histogram where the x-axis points are 40, 50, 60, 70, 80 and the intervals are 40-50, 50-60, 60-70, 70-80. The height of the rectangles for the intervals should be 3, 4, 7, 6 respectively.
Explanation / Answer
Answer:
import stdlib.StdDraw;
import stdlib.StdIn;
public class MakeHistogram {
public static void main(String[] args) {
// read input values
int N = StdIn.readInt();
int left = StdIn.readInt();
int right = StdIn.readInt();
// take an array to collect samples between the ranges
double[] samples = make_samples(left, right);
// make a array intervals[] include N entry
// intervals[i] is the ith interval between (l, r)
// every time value indicate number of intervals
// that fall in this interval
int[] intervals = fillSamplesInIntervals(samples, N, left, right);
// draw histogram
draw_histogram(intervals, samples);
}
public static double[] make_samples(int left, int right) {
String allstr = "";
while(!StdIn.isEmpty()) {
String str = StdIn.readString();
double n = Double.parseDouble(str);
if (n >= left && n <= right) {
allstr = allstr + str + " ";
}
}
String[] str_array = allstr.split(" ");
int len = str_array.length;
double[] double_array = new double[len];
for (int i = 0; i < len; i++) {
double_array[i] = Double.parseDouble(str_array[i]);
}
return double_array;
}
public static int[] fillSamplesInIntervals(double[] samples, int N, double left, double right) {
int[] result = new int[N];
int p;
for (int i = 0; i < samples.length; i++) {
p = findIntervalIndex(samples[i], N, left, right);
result[p] += 1;
}
return result;
}
public static int findIntervalIndex(double sample, int N, double left, double right) {
int k = 0;
double avg = (right - left) / N;
for (int i = 0; i < N; i++) {
if (sample >= avg * i && sample < avg * (i + 1)) {
k = i;
break;
}
}
// edge condition
if (sample == right) {
k = N - 1;
}
return k;
}
public static void draw_histogram(int[] intervals, double[] samples) {
StdDraw.setPenRadius(.006);
StdDraw.line(0, 0, 1, 0);
StdDraw.line(0, 0, 0, 1);
int n = intervals.length;
int total = samples.length;
double interval_width = 1.0 / n;
double x, y;
double halfWidth = interval_width / 2;
StdDraw.setPenColor(StdDraw.GRAY);
StdDraw.setPenRadius();
for (int i = 0; i < n; i++) {
x = i * interval_width + halfWidth;
y = (double)intervals[i] / total / 2;
StdDraw.rectangle(x, y, halfWidth, y);
}
}
}
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.