finding point of intersection in R

by

If you literally just have two random vectors of numbers, you can use a pretty simple technique to get the intersection of both. Just find all points where x1 is above x2, and then below it on the next point, or vice-versa. These are the intersection points. Then just use the respective slopes to find the intercept for that segment.

set.seed(2)
x1 <- sample(1:10, 100, replace = TRUE)
x2 <- sample(1:10, 100, replace = TRUE)

# Find points where x1 is above x2.
above <- x1 > x2

# Points always intersect when above=TRUE, then FALSE or reverse
intersect.points <- which(diff(above) != 0)

# Find the slopes for each line segment.
x1.slopes <- x1[intersect.points+1] - x1[intersect.points]
x2.slopes <- x2[intersect.points+1] - x2[intersect.points]

# Find the intersection for each segment.
x.points <- intersect.points + ((x2[intersect.points] - x1[intersect.points]) / (x1.slopes-x2.slopes))
y.points <- x1[intersect.points] + (x1.slopes*(x.points-intersect.points))

# Joint points
joint.points <- which(x1 == x2)
x.points <- c(x.points, joint.points)
y.points <- c(y.points, x1[joint.points])

# Plot points
plot(x1,type="l")
lines(x2,type="l",col="red")
points(x.points,y.points,col="blue")

# Segment overlap
start.segment <- joint.points[-1][diff(joint.points) == 1] - 1
for (i in start.segment) lines(x = c(i, i+1), y = x1[c(i, i+1)], col="blue")

enter image description here

More Related Contents:

  1. Finding where two linear fits intersect in R
  2. How to replace a value by another within a variable in R?
  3. Relative frequencies / proportions with dplyr
  4. How to add texture to fill colors in ggplot2
  5. Cleaning up factor levels (collapsing multiple levels/labels)
  6. Split a large dataframe into a list of data frames based on common value in column
  7. Save a plot in an object
  8. How to cbind or rbind different lengths vectors without repeating the elements of the shorter vectors?
  9. lapply vs for loop – Performance R
  10. ggplot, facet, piechart: placing text in the middle of pie chart slices
  11. YAML current date in rmarkdown
  12. Create new variables with mutate_at while keeping the original ones
  13. R: use magrittr pipe operator in self written package
  14. How to interpret dplyr message `summarise()` regrouping output by ‘x’ (override with `.groups` argument)?
  15. How to index a vector sequence within a vector sequence
  16. Convert seconds to days: hours:minutes:seconds
  17. Concatenate strings and expressions in a plot’s title
  18. Counting number of instances of a condition per row R [duplicate]
  19. Create a ranking variable with dplyr?
  20. Find value corresponding to maximum in other column [duplicate]
  21. Split delimited single value character vector
  22. R split numeric vector at position
  23. Creating a Plot Window of a Particular Size
  24. R: invalid multibyte string [duplicate]
  25. Reordering factor gives different results, depending on which packages are loaded
  26. Join two data frames in R based on closest timestamp
  27. Update/Replace Values in Dataframe with Tidyverse Join
  28. New R-Studio version 0.98.932 deletes .md file – how to prevent?
  29. how to debug “factor has new levels” error for linear model and prediction [duplicate]
  30. group by two columns in ggplot2

Leave a Comment