Your task: Create and evaluate the many types of clustering methods.
Code: Code of the airport;Airport: Name of the airport;Ordem: ID of the observations;Passengers: Number of passengers;Movements: Number of flights;Numberofairlines: Number of airlines in each airport;Mainairlineflightspercentage: Percentage of flights of the main airline of each airport;Maximumpercentageoftrafficpercountry: Maximum percentage of flights per country;NumberofLCCflightsweekly: Number of weekly low cost flights`;NumberofLowCostAirlines: Number of low cost airlines of each airport;LowCostAirlinespercentage: Percentage of the number of low cost airlines in each airport;Destinations: Number of flights arriving at each airport;Average_route_Distance: Average route distance in km;DistancetoclosestAirport: Distance to closest airport in kmDistancetoclosestSimilarAirport: Distance to closest similar airport in km;AirportRegionalRelevance: Relevance of the airport in a regional scale (0 - 1);Distancetocitykm: Distance between the airport and the city in km;Inhabitantscorrected: Population of the city;numberofvisitorscorrected: Number of vistors that arrived in the airport;GDP corrected: Corrected value of the Gross Domestic Product;Cargoton: Cargo ton. The total number of cargo transported in a certain period multiplied by the number o flights.
library(readxl) # Reading excel files
library(skimr) # Summary statistics
library(tidyverse) # Pack of useful tools
library(mclust) # Model based clustering
library(cluster) # Cluster analysis
library(factoextra) # Visualizing distancesdataset <- read_excel("Data/Data_Aeroports_Clustersv1.xlsX")
df <- data.frame(dataset)skim(df)| Name | df |
| Number of rows | 32 |
| Number of columns | 21 |
| _______________________ | |
| Column type frequency: | |
| character | 2 |
| numeric | 19 |
| ________________________ | |
| Group variables | None |
Data summary
Variable type: character
| skim_variable | n_missing | complete_rate | min | max | empty | n_unique | whitespace |
|---|---|---|---|---|---|---|---|
| Code | 0 | 1 | 3 | 3 | 0 | 32 | 0 |
| Airport | 0 | 1 | 4 | 35 | 0 | 32 | 0 |
Variable type: numeric
| skim_variable | n_missing | complete_rate | mean | sd | p0 | p25 | p50 | p75 | p100 | hist |
|---|---|---|---|---|---|---|---|---|---|---|
| Ordem | 0 | 1 | 16.50 | 9.38 | 1.00 | 8.75 | 16.50 | 24.25 | 32.00 | ▇▇▇▇▇ |
| Passengers | 0 | 1 | 20750710.88 | 17601931.34 | 456698.00 | 8927021.50 | 17275317.50 | 28666511.50 | 67054745.00 | ▇▅▂▂▁ |
| Movements | 0 | 1 | 205111.16 | 143564.45 | 5698.00 | 82765.75 | 191742.50 | 258654.50 | 518018.00 | ▇▅▇▂▃ |
| Numberofairlines | 0 | 1 | 57.81 | 40.42 | 1.00 | 22.50 | 55.50 | 90.25 | 136.00 | ▇▆▅▆▃ |
| Mainairlineflightspercentage | 0 | 1 | 33.78 | 22.08 | 12.00 | 22.00 | 28.50 | 33.00 | 95.00 | ▇▆▁▁▂ |
| Maximumpercentageoftrafficpercountry | 0 | 1 | 17.47 | 7.31 | 9.00 | 12.00 | 15.00 | 22.25 | 35.00 | ▇▂▃▂▂ |
| NumberofLCCflightsweekly | 0 | 1 | 397.59 | 221.56 | 37.00 | 226.25 | 366.50 | 546.75 | 776.00 | ▅▇▅▅▆ |
| NumberofLowCostAirlines | 0 | 1 | 11.59 | 5.60 | 1.00 | 7.75 | 12.00 | 16.00 | 23.00 | ▃▇▇▆▃ |
| LowCostAirlinespercentage | 0 | 1 | 36.44 | 30.10 | 6.25 | 16.29 | 19.59 | 50.36 | 100.00 | ▇▂▁▁▂ |
| Destinations | 0 | 1 | 167.62 | 80.13 | 20.00 | 109.25 | 168.50 | 222.50 | 301.00 | ▃▇▆▇▆ |
| Average_Route_Distance | 0 | 1 | 2275.19 | 930.28 | 1225.00 | 1599.50 | 2152.00 | 2765.00 | 5635.00 | ▇▆▂▁▁ |
| DistancetoclosestAirport | 0 | 1 | 90.19 | 64.56 | 13.84 | 45.83 | 66.50 | 111.61 | 244.50 | ▇▇▃▁▂ |
| DistancetoclosestSimilarAirport | 0 | 1 | 248.64 | 183.60 | 38.16 | 97.74 | 206.12 | 376.15 | 635.05 | ▇▅▃▁▃ |
| AirportRegionalrelevance | 0 | 1 | 0.73 | 0.23 | 0.19 | 0.58 | 0.80 | 0.91 | 0.99 | ▁▃▁▆▇ |
| Distancetocitykm | 0 | 1 | 25.81 | 25.44 | 3.00 | 9.75 | 14.50 | 35.00 | 100.00 | ▇▂▁▁▁ |
| Inhanbitantscorrected | 0 | 1 | 4528561.95 | 2590542.88 | 329240.50 | 2856960.30 | 4532760.00 | 6733158.88 | 9870818.00 | ▆▆▇▇▁ |
| numberofvisitorscorrected | 0 | 1 | 2766002.58 | 2549773.72 | 80232.50 | 1018390.89 | 1896295.60 | 3450491.78 | 9732062.00 | ▇▃▁▂▁ |
| GDPcorrected | 0 | 1 | 30160.75 | 10510.93 | 8500.00 | 25000.00 | 31150.00 | 35550.00 | 56600.00 | ▃▅▇▃▁ |
| Cargoton | 0 | 1 | 236531.76 | 478310.12 | 0.00 | 10325.00 | 72749.85 | 153372.85 | 1819000.00 | ▇▁▁▁▁ |
Now let us plot an example and take a look
plot(Numberofairlines ~ Destinations, df) #plot
text(Numberofairlines ~ Destinations, df, label = Airport, pos = 4, cex = 0.6) #labels over the previous plot
By looking at the plot, you may already have a clue on the number of clusters with this two variables. However, this is not clear and it does not consider the other variables in the analysis.
table(is.na(df))##
## FALSE
## 672
In this example we do not have missing values. In case you do have in
the future, you can take out the missing values with listwise deletion
(df <- na.omit(df)) or use other ways of treating missing values.
Leave only continuous variables, and make Ordem as the row ID variable
df_reduced = df[,!(names(df) %in% c("Code","Airport"))]
df_reduced = data.frame(df_reduced, row.names = 1) #Ordem is the 1st variable in the dfTake a look at the scale of the variables. See how they are different!
head(df_reduced)## Passengers Movements Numberofairlines Mainairlineflightspercentage
## 1 9830987 119322 64 18
## 2 9742300 132200 29 33
## 3 9155665 101557 47 17
## 4 9139479 74281 35 29
## 5 9129053 83013 11 37
## 6 8320927 115934 36 31
## Maximumpercentageoftrafficpercountry NumberofLCCflightsweekly
## 1 20 256
## 2 13 351
## 3 26 259
## 4 23 300
## 5 22 227
## 6 14 341
## NumberofLowCostAirlines LowCostAirlinespercentage Destinations
## 1 18 28.12500 104
## 2 12 41.37931 189
## 3 19 40.42553 116
## 4 18 51.42857 160
## 5 8 72.72727 87
## 6 7 19.44445 111
## Average_Route_Distance DistancetoclosestAirport
## 1 1253 23.66681
## 2 1721 63.45766
## 3 3143 122.58936
## 4 1701 63.09924
## 5 1582 45.13247
## 6 1460 244.49577
## DistancetoclosestSimilarAirport AirportRegionalrelevance Distancetocitykm
## 1 223.83824 0.8698581 6
## 2 63.45766 0.5127419 15
## 3 132.45082 0.7840877 19
## 4 134.50558 0.8098081 9
## 5 45.13247 0.1947903 55
## 6 559.31000 0.9810450 10
## Inhanbitantscorrected numberofvisitorscorrected GDPcorrected Cargoton
## 1 3551805.0 2152829.8 26300 11223.39
## 2 4180133.5 1151381.6 30100 562.00
## 3 705807.8 1678968.6 20700 25994.00
## 4 1508358.6 1944196.8 25000 3199.73
## 5 1562709.8 181063.5 32000 28698.00
## 6 6626197.0 770720.5 11200 82756.54
Z-score standardization: (xi − xmean)/σ
mean <- apply(df_reduced, 2, mean) # The "2" in the function is used to select the columns. MARGIN: c(1,2)
sd <- apply(df_reduced, 2, sd)
df_scaled <- scale(df_reduced, mean, sd)distance <- dist(df_scaled, method = "euclidean")Note: There are other forms of distance measures that can be used such as:
i) Minkowski distance; ii) Manhattan distance; iii) Mahanalobis distance.
fviz_dist(distance, gradient = list(low = "#00AFBB", mid = "white", high = "#FC4E07"), order = FALSE)
There are many types of hierarchical clustering. Let’s explore some.
1. Single linkage (nearest neighbor) clustering algorithm
Based on a bottom-up approach, by linking two clusters that have the closest distance between each other.
models <- hclust(distance, "single")
plot(models, labels = df$Airport, xlab = "Distance - Single linkage", cex=0.6, hang = -1)
rect.hclust(models, 4, border = "purple") # Visualize the cut on the dendogram, with 4 clusters
2. Complete linkage (Farthest neighbor) clustering algorithm
Complete linkage is based on the maximum distance between observations in each cluster.
modelc <- hclust(distance, "complete")
plot(modelc, labels = df$Airport, xlab = "Distance - Complete linkage", cex=0.6, hang = -1)
rect.hclust(modelc, 4, border = "blue") 
3. Average linkage between groups
The average linkage considers the distance between clusters to be the average of the distances between observations in one cluster to all the members in the other cluster.
modela <- hclust(distance, "average")
plot(modela, labels = df$Airport, xlab = "Distance - Average linkage", cex=0.6, hang = -1)
rect.hclust(modelc, 4, border = "red")
4. Ward`s method
The Ward`s method considers the measures of similarity as the sum of squares within the cluster summed over all variables.
modelw <- hclust(distance, "ward.D2")
plot(modelw, labels = df$Airport, xlab = "Distance - Ward method", cex=0.6, hang = -1)
rect.hclust(modelw, 4, border = "orange")
5. Centroid method
The centroid method considers the similarity between two clusters as the distance between its centroids.
modelcen <- hclust(distance, "centroid")
plot(modelcen, labels = df$Airport, xlab = "Distance - Centroid method", cex=0.6, hang = -1)
rect.hclust(modelcen, 4, border = "darkgreen")
Now lets evaluate the membership of each observation with the
cutree function for each method.
member_single <- cutree(models, 4)
member_com <- cutree(modelc, 4)
member_av <- cutree(modela, 4)
member_ward <- cutree(modelw, 4)
member_cen <- cutree(modelcen, 4)Compare how common each method is to each other.
table(member_com, member_av) # compare the complete linkage with the average linkage## member_av
## member_com 1 2 3 4
## 1 14 0 0 0
## 2 11 0 0 0
## 3 0 3 0 0
## 4 0 0 3 1
Note: Try comparing other methods, and evaluate how common they are.
The silhouette plot evaluates how similar an observation is to its own cluster compared to other clusters. The clustering configuration is appropriate when most objects have high values. Low or negative values indicate that the clustering method is not appropriate or the number of clusters is not ideal.
plot(silhouette(member_single, distance))
plot(silhouette(member_com, distance))
plot(silhouette(member_av, distance))
plot(silhouette(member_ward, distance))
plot(silhouette(member_cen, distance))
- k-means with n=3 clusters
km_clust <- kmeans(df_scaled, 3)
km_clust #print the results## K-means clustering with 3 clusters of sizes 7, 18, 7
##
## Cluster means:
## Passengers Movements Numberofairlines Mainairlineflightspercentage
## 1 -0.9456035 -1.0500969 -1.239468064 1.4006677
## 2 -0.2469314 -0.2011272 -0.004982515 -0.3699491
## 3 1.5805700 1.5672811 1.252280245 -0.4493699
## Maximumpercentageoftrafficpercountry NumberofLCCflightsweekly
## 1 0.9913460 -1.21033588
## 2 -0.1629508 0.04370786
## 3 -0.5723298 1.09794424
## NumberofLowCostAirlines LowCostAirlinespercentage Destinations
## 1 -1.2287547 1.4725164 -1.31999250
## 2 0.3305562 -0.2689855 0.07609389
## 3 0.3787531 -0.7808392 1.12432250
## Average_Route_Distance DistancetoclosestAirport
## 1 -0.8907198 0.20629602
## 2 -0.1062034 0.06631895
## 3 1.1638144 -0.37683045
## DistancetoclosestSimilarAirport AirportRegionalrelevance Distancetocitykm
## 1 -0.67596963 -0.9617675 1.0125397
## 2 -0.07737412 0.1407640 -0.3136475
## 3 0.87493166 0.5998030 -0.2060176
## Inhanbitantscorrected numberofvisitorscorrected GDPcorrected Cargoton
## 1 -0.92990235 -0.7382133 -0.5168124 -0.4251367
## 2 -0.06258292 -0.2290652 -0.1117858 -0.3186842
## 3 1.09082987 1.3272381 0.8042615 1.2446104
##
## Clustering vector:
## 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
## 2 2 2 2 1 2 2 1 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 2 2
## 27 28 29 30 31 32
## 1 1 2 1 1 1
##
## Within cluster sum of squares by cluster:
## [1] 67.16167 150.32291 70.90186
## (between_SS / total_SS = 48.3 %)
##
## Available components:
##
## [1] "cluster" "centers" "totss" "withinss" "tot.withinss"
## [6] "betweenss" "size" "iter" "ifault"
- Other ways of setting the number of clusters
This algorithm will detect how many clusters from 1 to 10 explains more variance
k <- list()
for(i in 1:10){
k[[i]] <- kmeans(df_scaled, i)
}Note: Try printing the k value and take a look at the ratio
between_SS/total_SS. Evaluate how it varies when you add clusters.
Now, let’s plot between_SS / total_SS into a scree plot
betSS_totSS <- list()
for(i in 1:10){
betSS_totSS[[i]] <- k[[i]]$betweenss/k[[i]]$totss
}
plot(1:10, betSS_totSS, type = "b", ylab = "Between SS / Total SS", xlab = "Number of clusters")
Let’s take out the outliers and see the difference in the k-means clustering:
- Examine the boxplots
par(cex.axis=0.6, mar=c(11,2,1,1))# Make labels fit in the boxplot
boxplot(df_scaled, las = 2) #labels rotated to vertical
- Detect the outliers
outliers <- boxplot.stats(df_scaled)$out
outliers## [1] 2.630622 2.772024 2.772024 3.611626 2.916185 2.523102 2.732030 2.515406
## [9] 3.308457 3.285459
- Remove rows with outliers
nrow(df_scaled) #32## [1] 32
out_ind <- which(df_scaled %in% c(outliers)) #the row.names that contain outliers
df_no_outliers = df_scaled[-c(out_ind),] #remove those rows from the df_scaled
nrow(df_no_outliers) #31## [1] 31
Note: There are many methods to treat outliers. This is just one of them. Note that it is not very appropriate, since it removes many observations that are relevant for the analysis. Try using other methods and evaluate the difference.
Execute a k-means clustering with the dataset without the outliers and see the difference.
km_no_outliers <- kmeans(df_no_outliers, 3)
km_no_outliers## K-means clustering with 3 clusters of sizes 5, 9, 17
##
## Cluster means:
## Passengers Movements Numberofairlines Mainairlineflightspercentage
## 1 -0.9520429 -1.0882984 -1.3214660 1.9931973
## 2 1.0324987 1.1325696 1.1976935 -0.5384938
## 3 -0.4213469 -0.3839557 -0.3053483 -0.2964051
## Maximumpercentageoftrafficpercountry NumberofLCCflightsweekly
## 1 0.64733736 -1.2772631
## 2 -0.53540967 0.8212658
## 3 0.08878316 -0.1595867
## NumberofLowCostAirlines LowCostAirlinespercentage Destinations
## 1 -1.39205703 1.9302799 -1.4105623
## 2 0.74731744 -0.7009284 0.9906072
## 3 0.06205453 -0.1392452 -0.1303986
## Average_Route_Distance DistancetoclosestAirport
## 1 -0.9635706 0.2765206
## 2 0.4884224 -0.3177118
## 3 -0.1876220 0.1279239
## DistancetoclosestSimilarAirport AirportRegionalrelevance Distancetocitykm
## 1 -0.71705981 -1.2364486 1.69762721
## 2 0.62904380 0.4413958 -0.06251112
## 3 -0.05722116 0.1511388 -0.45739254
## Inhanbitantscorrected numberofvisitorscorrected GDPcorrected Cargoton
## 1 -0.9802943 -0.7587213 -0.3558915 -0.4142745
## 2 1.0350785 0.9158328 0.3663198 0.6945365
## 3 -0.3212664 -0.3974202 -0.2372251 -0.3766378
##
## Clustering vector:
## 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 19 20 21 22 23 24 25 26 27
## 3 3 3 3 1 3 3 3 3 3 3 3 3 3 2 3 3 2 2 2 2 2 2 2 2 1
## 28 29 30 31 32
## 1 3 3 1 1
##
## Within cluster sum of squares by cluster:
## [1] 41.82151 83.73019 140.39960
## (between_SS / total_SS = 47.7 %)
##
## Available components:
##
## [1] "cluster" "centers" "totss" "withinss" "tot.withinss"
## [6] "betweenss" "size" "iter" "ifault"
Finally, plot the clusters results to check if they make sense.
Let us go back to first example and take a look.
- K-means with outliers
plot(Numberofairlines ~ Destinations, df, col = km_clust$cluster)
with(df, text(Numberofairlines ~ Destinations, label = Airport, pos = 1, cex = 0.6))
- K-means without outliers
plot(Numberofairlines ~ Destinations, df, col = km_no_outliers$cluster)
with(df, text(Numberofairlines ~ Destinations, label = Airport, pos = 1, cex = 0.6))