# Plotting Indifference Curves with R Contour Function

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The following post at Constructing Difference Curves – Part 3 from economics.about.com provides a discussion on indifference curves (but actually I think they are isoquants) and how to construct them. I think I have a grasp on how to do this in R if you define the utility function as z = √(x*y) . For the x and y data I used modified data from the article mentioned above, and then plotted some simulated data.**Econometric Sense**, and kindly contributed to R-bloggers]. (You can report issue about the content on this page here)Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.

The data I used for x and y (which I modified-see documentation in the R-code) is listed below:

x: 1,2,3,4,5,6,7,8

y: 10,10,10,15,15,30,60,90

The R code below reads in the data and plots level sets or indifference curves for both the data above and the simulated data. This very basic, for full documentation ( and options for x,y limits, levels etc.) of the contour function in R see here.

Edit: for the second part of the program, if I switch the values of x and y I get indifference curves that are convex to the origin as they should be- the correction can be also represented much more compactly as:

contour( xyT<-t(as.matrix(cbind(x<-seq(0,20,by=2),y<-seq(0,100,by=10)))), z<-as.matrix(sqrt(x*y)) )

See program below:

# *------------------------------------------------------------------ # | PROGRAM NAME: INDIFFERENCE_CURVES_R # | DATE: 3/11/11 # | CREATED BY: MATT BOGARD # | PROJECT FILE: P:\R Code References # *---------------------------------------------------------------- # | PURPOSE: MORE TO PLOT LEVEL SETS USING THE CONTOUR FUNCTION THAN # | TO ACTUALLY PLOT INDIFFERENCE CURVES # *------------------------------------------------------------------ # | COMMENTS: # | # | 1: references: http://stat.ethz.ch/R-manual/R-devel/library/graphics/html/contour.html # | 2: # | 3: # |*------------------------------------------------------------------ # | DATA USED: http://economics.about.com/od/indifferencecurves/a/constructing3.htm # | # | # |*------------------------------------------------------------------ # | CONTENTS: # | # | PART 1: explicit data # | PART 2: simulated data (sort of) - not really indifference curves # | PART 3: # *----------------------------------------------------------------- # | UPDATES: # | # | # *------------------------------------------------------------------ # *------------------------------------------------------------------ # | PART 1: explicit data # *----------------------------------------------------------------- # raw data x <- c(1,2,3,4,5,6,7,8) y <- c(10,10,10,15,15,30,60,90) # note- for the contour function to work below, x and y # These must be in ascending order-based on the contour documentation # which is the opposite of how the data was presented at # about.com # put x and y in a matrix xy <- as.matrix(cbind(x,y)) # transpose xy xyT <- t(xy) # define function z as a matrix z <- as.matrix(sqrt(x*y)) # plot the countour plot / specified level sets contour(xyT,z) # all levels contour(xyT,z, levels =c(10,20,50)) # specified levels for z # *------------------------------------------------------------------ # | PART 2: simulated data (sort of) - not really indifference curves # *----------------------------------------------------------------- rm(list=ls()) # get rid of any existing data ls() # display active data -should be null # define x and y x <- seq(0,100,by=10) y <- seq(0,20,by=2) # put x and y in a matrix xy <- as.matrix(cbind(x,y)) # transpose xy xyT <- t(xy) # define function z as a matrix z <- as.matrix(sqrt(x*y)) contour(xyT,z)

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