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Sequence Plots: heatmap, index, and distribution

Mohammed Saqr

University of Eastern Finland

Sonsoles López-Pernas

University of Eastern Finland

Kamila Misiejuk

FernUniversität in Hagen, Germany
Source: vignettes/sequence-plots.Rmd
sequence-plots.Rmd

The dataset

trajectories ships with Nestimate: 138 student sequences × 15 weeks, three states (Active, Average, Disengaged) plus NA for missed weeks.

data(trajectories)
dim(trajectories)
#> [1] 138  15
head(trajectories[, 1:8])
#>      1         2            3            4            5            6           
#> [1,] "Active"  "Disengaged" "Disengaged" "Disengaged" "Active"     "Active"    
#> [2,] "Average" "Average"    "Average"    "Average"    "Average"    "Average"   
#> [3,] "Average" "Active"     "Active"     "Active"     "Active"     "Active"    
#> [4,] "Active"  "Active"     "Active"     "Active"     "Active"     "Average"   
#> [5,] "Active"  "Active"     "Active"     "Average"    "Active"     "Average"   
#> [6,] "Average" "Average"    "Disengaged" "Average"    "Disengaged" "Disengaged"
#>      7         8        
#> [1,] "Active"  "Active" 
#> [2,] "Average" "Average"
#> [3,] "Active"  "Active" 
#> [4,] "Average" "Active" 
#> [5,] "Active"  "Active" 
#> [6,] "Average" "Average"
sort(unique(as.vector(trajectories)), na.last = NA)
#> [1] "Active"     "Average"    "Disengaged"

sequence_plot() is the single entry point for three views of this data:

type What it shows Uses dendrogram? Facets?
"heatmap" (default) dense carpet, rows sorted by a distance/dendrogram yes no
"index" carpet without dendrogram, row-gap optional no yes
"distribution" stacked area / bar of state proportions over time no yes

Defaults: legend = "right", frame = FALSE.

1. type = "heatmap" — clustered carpet

1.1 Default — LCS distance, ward.D2 dendrogram 

sequence_plot(trajectories)

1.2 Switch the sort strategy 

sequence_plot(trajectories, sort = "frequency",
              main = "sort = 'frequency'")

sequence_plot(trajectories, sort = "hamming",
              main = "sort = 'hamming'")

sequence_plot(trajectories, sort = "start",
              main = "sort = 'start' (no dendrogram)")

Available sorts: lcs (default), frequency, start, end, plus any build_clusters() distance — hamming, osa, lv, dl, qgram, cosine, jaccard, jw.

1.3 Cluster separators with k

Cut the dendrogram into k groups and overlay thin horizontal lines at the cluster boundaries in the ordered rows. Tune with k_color and k_line_width.

sequence_plot(trajectories, k = 3,
              main = "k = 3 — white separators")

sequence_plot(trajectories, k = 5,
              k_color = "black", k_line_width = 1.2,
              main = "k = 5 — thin black")

1.4 Legend position, custom palette, title 

sequence_plot(trajectories,
              legend = "bottom",
              legend_title = "Engagement",
              state_colors = c("#2a9d8f", "#e9c46a", "#e76f51"),
              main = "Custom palette + bottom legend")

1.5 Cell borders + tick thinning 

sequence_plot(trajectories,
              cell_border = "grey60", tick = 3,
              main = "Cell grid + every-3rd tick")

1.6 frame = TRUE brings back the outer box 

sequence_plot(trajectories, frame = TRUE,
              main = "frame = TRUE")

2. type = "index" — gap-ready carpet with facets

No dendrogram. Rows are sorted within each panel by sort. Supports group (vector or auto from a net_clustering) plus ncol / nrow facet grids.

2.1 Single panel 

sequence_plot(trajectories, type = "index",
              main = "index — single panel")

2.2 Visible row gaps 

sequence_plot(trajectories, type = "index", row_gap = 0.25,
              main = "index with row_gap = 0.25")

2.3 Faceted by net_clustering (auto 2×2 for k = 3) 

cl <- build_clusters(trajectories, k = 3L,
                   dissimilarity = "hamming", method = "ward.D2")
sequence_plot(cl, type = "index",
              main = "index faceted by build_clusters(k = 3)")

2.4 Force a 1×3 row 

sequence_plot(cl, type = "index", ncol = 3, nrow = 1,
              main = "index — ncol = 3, nrow = 1")

3. type = "distribution" — state proportions over time

Stacked area or bar chart of state frequencies per time column.

3.1 Default stacked area 

sequence_plot(trajectories, type = "distribution",
              main = "distribution — stacked area")

3.2 Stacked bars, count scale 

sequence_plot(trajectories, type = "distribution",
              geom = "bar", scale = "count",
              main = "distribution — bars, count scale")

3.3 NA band on/off 

sequence_plot(trajectories, type = "distribution", na = TRUE,
              main = "na = TRUE")

sequence_plot(trajectories, type = "distribution", na = FALSE,
              main = "na = FALSE")

3.4 Faceted by cluster 

sequence_plot(cl, type = "distribution",
              main = "distribution by cluster (k = 3)")

Cheat sheet 

# Always explore first with the default:
sequence_plot(trajectories)


# Zoom in on cluster structure:
sequence_plot(trajectories, k = 3)

sequence_plot(trajectories, sort = "hamming", k = 4)


# Compare cluster compositions:
cl <- build_clusters(trajectories, k = 3,
                   dissimilarity = "hamming", method = "ward.D2")
sequence_plot(cl, type = "index")

sequence_plot(cl, type = "distribution")


# Polish for a paper:
sequence_plot(trajectories, k = 3,
              state_colors = c("#2a9d8f", "#e9c46a", "#e76f51"),
              legend_title = "Engagement",
              legend = "bottom",
              cell_border = "grey70",
              main = "Student engagement trajectories")