Matias Salibian-Barrera & Graciela Boente 2025-12-04
This repository contains the sparseFPCA package that implements the
robust FPCA method introduced in Robust functional principal components
for sparse longitudinal
data (Boente and
Salibian-Barrera, 2021) (ArXiv).
LICENSE: The content in this repository is released under the “Creative Commons Attribution-ShareAlike 4.0 International” license. See the human-readable version here and the real thing here.
The sparseFPCA package implements the robust functional principal
components analysis (FPCA) estimator introduced in Boente and
Salibian-Barrera, 2021.
sparseFPCA computes robust estimators for the mean and covariance
(scatter) functions, and the corresponding eigenfunctions. It can be
used with functional data sets where only a few observations per curve
are available (possibly recorded at irregular intervals).
The package can be installed directly from this repository using the
following command in R:
devtools::install_github('msalibian/sparseFPCA', ref = "master")Here we illustrate the use of our method and compare it with existing
alternatives. We will analyze the CD4 data, which is available in the
catdata package
(catdata). These data are
part of the Multicentre AIDS Cohort Study (Zeger and Diggle,
1994). They consist of 2376
measurements of CD4 cell counts, taken on 369 men. The times are
measured in years since seroconversion (t = 0).
We first load the data set and arrange it in a suitable format. Because
the data consist of trajectories of different lengths, possibly measured
at different times, the software requires that the observations be
arranged in two lists, one (which we call X$x below) containing the
vectors (of varying lengths) of points observed in each curve, and the
other (X$pp) with the corresponding times:
data(aids, package='catdata')
X <- vector('list', 2)
names(X) <- c('x', 'pp')
X$x <- split(aids$cd4, aids$person)
X$pp <- split(aids$time, aids$person)To ensure that there are enough observations to estimate the covariance
function at every pair of times (s, t), we only consider observations
for which t >= 0, and remove individuals that only have one
measurement.
n <- length(X$x)
shorts <- vector('logical', n)
for(i in 1:n) {
tmp <- (X$pp[[i]] >= 0)
X$pp[[i]] <- (X$pp[[i]])[tmp]
X$x[[i]] <- (X$x[[i]])[tmp]
if( length(X$pp[[i]]) <= 1 ) shorts[i] <- TRUE
}
X$x <- X$x[!shorts]
X$pp <- X$pp[!shorts]This results in a data set with N = 292 curves, where the number of
observations per individual ranges between 2 and 11 (with a median of
5):
length(X$x)## [1] 292
summary(lens <- sapply(X$x, length))## Min. 1st Qu. Median Mean 3rd Qu. Max.
## 2.000 3.000 5.000 4.983 6.000 11.000
table(lens)## lens
## 2 3 4 5 6 7 8 9 10 11
## 51 52 35 43 39 20 23 10 15 4
The following figure shows the data set with three randomly chosen trajectories highlighted with solid black lines:
xmi <- min( tmp <- unlist(X$x) )
xma <- max( tmp )
ymi <- min( tmp <- unlist(X$pp) )
yma <- max( tmp )
n <- length(X$x)
plot(seq(ymi, yma, length=5), seq(xmi, xma,length=5), type='n', xlab='t', ylab='X(t)')
for(i in 1:n) { lines(X$pp[[i]], X$x[[i]], col='gray', lwd=1, type='b', pch=19,
cex=1) }
lens <- sapply(X$x, length)
set.seed(22)
ii <- c(sample((1:n)[lens==2], 1), sample((1:n)[lens==5], 1),
sample((1:n)[lens==10], 1))
for(i in ii) lines(X$pp[[i]], X$x[[i]], col='black', lwd=4, type='b', pch=19,
cex=1, lty=1)
We will compare the robust and non-robust versions of our approach with the PACE estimator of Yao, Muller and Wang (paper - package). We need to load the following packages
library(sparseFPCA)
library(doParallel)
library(fdapace)The specific versions of these packages that were used here (via the
output of the function sessionInfo()) can be found at the bottom of
this page.
The following are parameters required for our estimator.
ncpus <- 4
seed <- 123
rho.param <- 1e-3
max.kappa <- 1e3
ncov <- 50
k.cv <- 10
k <- 5
s <- k
hs.mu <- seq(.1, 1.5, by=.1)
hs.cov <- seq(1, 7, length=10)We now fit the robust and non-robust versions of our proposal, and also the PACE estimator. This step may take several minutes to run:
ours.ls <- lsfpca(X=X, ncpus=ncpus, hs.mu=hs.mu, hs.cov=hs.cov, rho.param=rho.param,
k = k, s = k, trace=FALSE, seed=seed, k.cv=k.cv, ncov=ncov,
max.kappa=max.kappa)
ours.r <- efpca(X=X, ncpus=ncpus, hs.mu=hs.mu, hs.cov=hs.cov, rho.param=rho.param,
alpha=0.2, k = k, s = k, trace=FALSE, seed=seed, k.cv=k.cv, ncov=ncov,
max.kappa=max.kappa)
myop <- list(error=FALSE, methodXi='CE', dataType='Sparse',
userBwCov = 1.5, userBwMu= .3, kernel='epan', verbose=FALSE, nRegGrid=50)
pace <- FPCA(Ly=X$x, Lt=X$pp, optns=myop)The coverage plot:
plot(ours.ls$ma$mt[,1], ours.ls$ma$mt[,2], pch=19, col='gray70', cex=.8,
xlab='s', ylab='t', cex.lab=1.2, cex.axis=1.1)
points(ours.ls$ma$mt[,1], ours.ls$ma$mt[,1], pch=19, col='gray70', cex=.8)
The estimated covariance functions:
ss <- tt <- ours.r$ss
G.r <- ours.r$cov.fun
filled.contour(tt, ss, G.r, main='ROB')
ss <- tt <- ours.ls$ss
G.ls <- ours.ls$cov.fun
filled.contour(tt, ss, G.ls, main='LS')
ss <- tt <- pace$workGrid
G.pace <- pace$smoothedCov
filled.contour(tt, ss, G.pace, main='PACE')
Another take:
persp(ours.r$tt, ours.r$ss, G.r, xlab="s", ylab="t", zlab=" ",
zlim=c(10000, 130000), theta = -30, phi = 30, r = 50,
col="gray90", ltheta = 120, shade = 0.15, ticktype="detailed",
cex.axis=0.9, main = 'ROB')
persp(ours.ls$tt, ours.ls$ss, G.ls, xlab="s", ylab="t", zlab=" ",
zlim=c(10000, 130000), theta = -30, phi = 30, r = 50,
col="gray90", ltheta = 120, shade = 0.15, ticktype="detailed",
cex.axis=0.9, cex.lab=.9, main = 'LS')
persp(pace$workGrid, pace$workGrid, G.pace, xlab="s", ylab="t", zlab=" ",
zlim=c(10000, 130000), theta = -30, phi = 30, r = 50,
col="gray90", ltheta = 120, shade = 0.15, ticktype="detailed",
cex.axis=0.9, main = 'PACE')
The “proportion of variance” explained by the first few principal directions are:
dd <- eigen(ours.r$cov.fun)$values
ddls <- eigen(ours.ls$cov.fun)$values
ddp <- eigen(pace$smoothedCov)$values
rbind(ours = cumsum(dd)[1:3] / sum(dd[dd > 0]),
ls = cumsum(ddls)[1:3] / sum(ddls[ddls > 0]),
pace = cumsum(ddp)[1:3] / sum(ddp[ddp > 0]))## [,1] [,2] [,3]
## ours 0.9467379 0.9983907 0.9998978
## ls 0.9524343 0.9894052 0.9994967
## pace 0.8774258 0.9480532 0.9731165
In what follows we will use 2 principal components. The corresponding estimated scores are:
colors <- c('skyblue2', 'tomato3', 'gray70') #ROB, LS, PACE
boxplot(cbind(ours.r$xis[, 1:2], ours.ls$xis[, 1:2], pace$xiEst[, 1:2]),
names = rep(1:2, 3), col=rep(colors, each=2))
abline(h=0, lwd=2)
abline(v=c(2.5, 4.5), lwd=2, lty=2)
axis(3, las=1, at=c(1.5,3.5,5.5), cex.axis=1.4, lab=c('ROB', 'LS', 'PACE'),
line=0.2, pos=NA, col="white")
We now compare the first two eigenfunctions.
G2 <- ours.r$cov.fun
G2.svd <- eigen(G2)$vectors
G.pace <- pace$smoothedCov
Gpace.svd <- eigen(G.pace)$vectors
G2.ls <- ours.ls$cov.fun
G2.ls.svd <- eigen(G2.ls)$vectors
ma <- -(mi <- -0.5) # y-axis limits
for(j in 1:2) {
phihat <- G2.svd[,j]
phipace <- Gpace.svd[,j]
phils <- G2.ls.svd[,j]
sg <- as.numeric(sign(phihat %*% phipace ))
phipace <- sg * phipace
sg <- as.numeric(sign(phihat %*% phils ))
phils <- sg * phils
tt <- unique(ours.r$tt)
tt.ls <- unique(ours.ls$tt)
tt.pace <- pace$workGrid
plot(tt, phihat, ylim=c(mi,ma), type='l', lwd=4, lty=1,
xlab='t', ylab=expression(hat(phi)), cex.lab=1.1,
main=paste0('Eigenfunction ', j))
lines(tt.ls, phils, lwd=4, lty=2)
lines(tt.pace, phipace, lwd=4, lty=3)
legend('topright', legend=c('Robust (ROB)', 'Non-robust (LS)',
'PACE'), lwd=2, lty=1:3)
}
We look for potential outliers, using the scores on the first two eigenfunctions.
kk <- 2
xis.r <- ours.r$xis[, 1:kk]
dist.ous <- RobStatTM::covRob(xis.r)$dist
ous <- (1:length(dist.ous))[ dist.ous > qchisq(.995, df=kk)]We look at the 5 most outlying curves, as flagged by the robust fit:
xmi <- min( tmp <- unlist(X$x) )
xma <- max( tmp )
ymi <- min( tmp <- unlist(X$pp) )
yma <- max( tmp )
ii <- 1:length(X$x)
plot(seq(ymi, yma, length=5), seq(xmi, xma,length=5), type='n', xlab='t', ylab='X(t)')
title(main='Most outlying')
for(i in ii) { lines(X$pp[[i]], X$x[[i]], col='gray', lwd=1, type='b', pch=19,
cex=1.2) }
ii4 <- order(dist.ous, decreasing=TRUE)[1:5]
for(i in ii4) lines(X$pp[[i]], X$x[[i]], col='black', lwd=3, type='b', pch=19, cex=1.2)
Note that these curves appear to either decrease too rapidly (with respect to the rest), or to remain at high values over time. In the following plot of all the outlying curves we note that they all show one of these two main patterns.
xmi <- min( tmp <- unlist(X$x) )
xma <- max( tmp )
ymi <- min( tmp <- unlist(X$pp) )
yma <- max( tmp )
ii <- 1:length(X$x)
plot(seq(ymi, yma, length=5), seq(xmi, xma,length=5), type='n',
xlab='t', ylab='X(t)')
for(i in ii) {
lines(X$pp[[i]], X$x[[i]], col='gray', lwd=1, type='b', pch=19,
cex=1.2)
}
cols <- rainbow(length(ous))
for(i in 1:length(ous)) {
lines(X$pp[[ous[i]]], X$x[[ous[i]]], col=cols[i], lwd=3, type='b',
pch=19, cex=1.2)
}
legend('topright', legend=ous, lty=1, lwd=2, col=cols, ncol=5, cex=0.8)
We now remove the outliers and re-fit the non-robust estimators:
X.clean <- X
X.clean$x <- X$x[ -ous ]
X.clean$pp <- X$pp[ -ous ]Now re-fit on the “clean” data:
ours.ls.clean <- lsfpca(X=X.clean, ncpus=ncpus, hs.mu=hs.mu, hs.cov=hs.cov,
rho.param=rho.param, k = k, s = k, trace=FALSE,
seed=seed, k.cv=k.cv, ncov=ncov, max.kappa=max.kappa)
myop.clean <- list(error=FALSE, methodXi='CE', dataType='Sparse',
userBwCov = 1.5, userBwMu= .3,
kernel='epan', verbose=FALSE, nRegGrid=50)
pace.clean <- FPCA(Ly=X.clean$x, Lt=X.clean$pp, optns=myop.clean)The estimated covariance functions:
ss <- tt <- ours.r$ss
G.r <- ours.r$cov.fun
filled.contour(tt, ss, G.r, main='ROB')
ss <- tt <- ours.ls.clean$ss
G.ls.clean <- ours.ls.clean$cov.fun
filled.contour(tt, ss, G.ls.clean, main='LS - Clean')
ss <- tt <- pace.clean$workGrid
G.pace.clean <- pace.clean$smoothedCov
filled.contour(tt, ss, G.pace.clean, main='PACE - Clean')
And:
persp(ours.r$ss, ours.r$ss, G.r, xlab="s", ylab="t", zlab=" ",
zlim=c(10000, 65000), theta = -30, phi = 30, r = 50, col="gray90",
ltheta = 120, shade = 0.15, ticktype="detailed", cex.axis=0.9, main ='ROB')
persp(ours.ls.clean$ss, ours.ls.clean$ss, G.ls.clean, xlab="s", ylab="t", zlab=" ",
zlim=c(10000, 65000), theta = -30, phi = 30, r = 50, col="gray90",
ltheta = 120, shade = 0.15, ticktype="detailed", cex.axis=0.9,
main = 'LS - Clean')
persp(pace.clean$workGrid, pace.clean$workGrid, G.pace.clean, xlab="s", ylab="t",
zlab=" ", zlim=c(10000, 65000), theta = -30, phi = 30, r = 50,
col="gray90", ltheta = 120, shade = 0.15, ticktype="detailed", cex.axis=0.9,
main = 'PACE - Clean')
We can also compare the eigenfunctions:
G2 <- ours.r$cov.fun
G2.svd <- eigen(G2)$vectors
G.pace.clean <- pace.clean$smoothedCov
Gpace.svd.clean <- eigen(G.pace.clean)$vectors
G2.ls.clean <- ours.ls.clean$cov.fun
G2.ls.svd.clean <- eigen(G2.ls.clean)$vectors
ma <- -(mi <- -0.5)
for(j in 1:2) {
phihat <- G2.svd[,j]
phipace <- Gpace.svd.clean[,j]
phils <- G2.ls.svd.clean[,j]
sg <- as.numeric(sign(phihat %*% phipace ))
phipace <- sg * phipace
sg <- as.numeric(sign(phihat %*% phils ))
phils <- sg * phils
tt <- unique(ours.r$tt)
tt.ls <- unique(ours.ls.clean$tt)
tt.pace <- pace.clean$workGrid
plot(tt, phihat, ylim=c(mi,ma), type='l', lwd=4, lty=1,
xlab='t', ylab=expression(hat(phi)), cex.lab=1.1)
lines(tt.ls, phils, lwd=4, lty=2)
lines(tt.pace, phipace, lwd=4, lty=3)
legend('topright', legend=c('Robust (ROB)', 'Non-robust (LS)',
'PACE'), lwd=2, lty=1:3)
}
In this section we look at the prediction performance of these FPCA methods. We will randomly split the data into a training set (80% of the curves) and a test set (remaining 20% of trajectories), and then use the estimates of the covariance function obtained with the training set to predict the curves of the held out individuals.
We first re-construct the data:
data(aids, package='catdata')
X <- vector('list', 2)
names(X) <- c('x', 'pp')
X$x <- split(aids$cd4, aids$person)
X$pp <- split(aids$time, aids$person)
n <- length(X$x)
shorts <- vector('logical', n)
for(i in 1:n) {
tmp <- (X$pp[[i]] >= 0)
X$pp[[i]] <- (X$pp[[i]])[tmp]
X$x[[i]] <- (X$x[[i]])[tmp]
if( length(X$pp[[i]]) <= 1 ) shorts[i] <- TRUE
}
X$x <- X$x[!shorts]
X$pp <- X$pp[!shorts]
X.all <- XWe now build the test and training sets. Note that we require that the range of times of the curves in the test set be strictly included in the range of times for the curves in the training set.
ok.sample <- FALSE
max.it <- 20000
set.seed(22)
it <- 1
n <- length(X.all$x)
while( !ok.sample && (it < max.it) ) {
it <- it + 1
X.test <- X <- X.all
ii <- sample(n, floor(n*.2))
X.test$x <- X.all$x[ii] # test set
X.test$pp <- X.all$pp[ii] # test set
X.test$trt <- X.all$trt[ii] # test set
X$x <- X.all$x[ -ii ] # training set
X$pp <- X.all$pp[ -ii ] # training set
X$trt <- X.all$trt[ -ii ]
empty.test <- (sapply(X.test$x, length) == 0)
empty.tr <- (sapply(X$x, length) == 0)
X$pp <- X$pp[!empty.tr]
X$x <- X$x[!empty.tr]
X.test$x <- X.test$x[ !empty.test ]
X.test$pp <- X.test$pp[ !empty.test ]
ra.tr <- range(unlist(X$pp))
ra.te <- range(unlist(X.test$pp))
ok.sample <- ( (ra.tr[1] < ra.te[1]) && (ra.te[2] < ra.tr[2]) )
}
if(!ok.sample) stop('Did not find good split')Now we calculate the three estimators on the training set, using the same settings as before (except for the bandwidth used to estimate the mean function, which is set to 0.3).
ncpus <- 4
seed <- 123
rho.param <- 1e-3
max.kappa <- 1e3
ncov <- 50
k.cv <- 10
k <- 5
s <- k
hs.cov <- seq(1, 7, length=10)
hs.mu <- .3
ours.r.tr <- efpca(X=X, ncpus=ncpus, hs.mu=hs.mu, hs.cov=hs.cov, rho.param=rho.param, alpha=0.2,
k = k, s = k, trace=FALSE, seed=seed, k.cv=k.cv, ncov=ncov, max.kappa=max.kappa)
ours.ls.tr <- lsfpca(X=X, ncpus=ncpus, hs.mu=hs.mu, hs.cov=hs.cov, rho.param=rho.param,
k = k, s = k, trace=FALSE, seed=seed, k.cv=k.cv, ncov=ncov, max.kappa=max.kappa)
myop <- list(error=FALSE, methodXi='CE', dataType='Sparse',
userBwCov = 1.5, userBwMu= .3,
kernel='epan', verbose=FALSE, nRegGrid=50)
pace.tr <- FPCA(Ly=X$x, Lt=X$pp, optns=myop)Next, using these estimated mean and covariance functions we construct predicted curves for the patients in the test set:
# pr2.pace <- predict(pace.tr, newLy = X.test$x, newLt=X.test$pp, K = ncol(pace.tr$xiEst), xiMethod='CE')
# pp.pace <- pace.tr$phi %*% t(pr2.pace)
pr2.pace <- predict(pace.tr, newLy = X.test$x, newLt=X.test$pp, K = ncol(pace.tr$xiEst), xiMethod='CE')
pp.pace <- pace.tr$phi %*% t(pr2.pace$scores)
tts <- unlist(X$pp)
mus <- unlist(ours.ls.tr$muh)
mu.fn <- approxfun(x=tts, y=mus)
mu.fn.ls <- mu.fn(ours.ls.tr$tt)
kk <- 2
pred.test.ls <- pred.cv.whole(X=X, muh=mu.fn.ls, X.pred=X.test,
muh.pred=ours.ls$muh[ii],
cov.fun=ours.ls.tr$cov.fun, tt=ours.ls.tr$tt,
k=kk, s=kk, rho=ours.ls.tr$rho.param)
tts <- unlist(X$pp)
mus <- unlist(ours.r.tr$muh)
mu.fn <- approxfun(x=tts, y=mus)
mu.fn.r <- mu.fn(ours.r.tr$tt)
pred.test.r <- pred.cv.whole(X=X, muh=mu.fn.r, X.pred=X.test,
muh.pred=ours.r$muh[ii],
cov.fun=ours.r.tr$cov.fun, tt=ours.r.tr$tt,
k=kk, s=kk, rho=ours.r.tr$rho.param)We now show 4 trajectories in the test set, along with the corresponding estimated curves:
xmi <- min( tmp <- unlist(X$x) )
xma <- max( tmp )
ymi <- min( tmp <- unlist(X$pp) )
yma <- max( tmp )
ii2 <- 1:length(X$x)
show.these <- c(4, 44, 46, 34)
for(j in show.these) {
plot(seq(ymi, yma, length=5), seq(xmi, xma,length=5), type='n', xlab='t', ylab='X(t)')
lines(X.test$pp[[j]], X.test$x[[j]], col='gray50', lwd=5, type='b', pch=19, cex=2)
lines(pace.tr$workGrid, pp.pace[,j] + pace.tr$mu, lwd=3, lty=3)
lines(ours.ls.tr$tt, pred.test.ls[[j]], lwd=3, lty=2)
lines(ours.r.tr$tt, pred.test.r[[j]], lwd=3, lty=1)
legend('topright', legend=c('Robust (ROB)', 'Non-robust (LS)', 'PACE'), lwd=2, lty=1:3)
}
version## _
## platform x86_64-w64-mingw32
## arch x86_64
## os mingw32
## crt ucrt
## system x86_64, mingw32
## status
## major 4
## minor 5.1
## year 2025
## month 06
## day 13
## svn rev 88306
## language R
## version.string R version 4.5.1 (2025-06-13 ucrt)
## nickname Great Square Root
sessionInfo()## R version 4.5.1 (2025-06-13 ucrt)
## Platform: x86_64-w64-mingw32/x64
## Running under: Windows 11 x64 (build 26200)
##
## Matrix products: default
## LAPACK version 3.12.1
##
## locale:
## [1] LC_COLLATE=English_Canada.utf8 LC_CTYPE=English_Canada.utf8
## [3] LC_MONETARY=English_Canada.utf8 LC_NUMERIC=C
## [5] LC_TIME=English_Canada.utf8
##
## time zone: America/Vancouver
## tzcode source: internal
##
## attached base packages:
## [1] parallel stats graphics grDevices utils datasets methods
## [8] base
##
## other attached packages:
## [1] fdapace_0.6.0 doParallel_1.0.17 iterators_1.0.14 foreach_1.5.2
## [5] sparseFPCA_0.0.0.1
##
## loaded via a namespace (and not attached):
## [1] RobStatTM_1.0.11 generics_0.1.4 stringi_1.8.7
## [4] lattice_0.22-7 pracma_2.4.6 digest_0.6.39
## [7] magrittr_2.0.4 evaluate_1.0.5 grid_4.5.1
## [10] RColorBrewer_1.1-3 fastmap_1.2.0 Matrix_1.7-3
## [13] nnet_7.3-20 backports_1.5.0 Formula_1.2-5
## [16] gridExtra_2.3 mgcv_1.9-3 scales_1.4.0
## [19] numDeriv_2016.8-1.1 codetools_0.2-20 cli_3.6.5
## [22] rlang_1.1.6 Hmisc_5.2-4 splines_4.5.1
## [25] base64enc_0.1-3 yaml_2.3.11 tools_4.5.1
## [28] checkmate_2.3.3 htmlTable_2.4.3 dplyr_1.1.4
## [31] colorspace_2.1-2 ggplot2_4.0.1 vctrs_0.6.5
## [34] R6_2.6.1 rpart_4.1.24 lifecycle_1.0.4
## [37] stringr_1.5.2 htmlwidgets_1.6.4 MASS_7.3-65
## [40] foreign_0.8-90 cluster_2.1.8.1 pkgconfig_2.0.3
## [43] pillar_1.11.1 gtable_0.3.6 data.table_1.17.8
## [46] glue_1.8.0 Rcpp_1.1.0 xfun_0.53
## [49] tibble_3.3.0 tidyselect_1.2.1 rstudioapi_0.17.1
## [52] knitr_1.50 farver_2.1.2 htmltools_0.5.8.1
## [55] nlme_3.1-168 rmarkdown_2.30 compiler_4.5.1
## [58] S7_0.2.1