Creating a pipeline in R that serially processes multiple csv files - r

Question

My pipeline reads in a csv to a dataframe, assigns rownames, removes a column, performs a pca, plots the pca and extracxts the meaningful variables from the pca which are also plotted.
Here is my current code, which only goes as far as the first plot:
library(ggplot2)
library(ggrepel)
tsv = read.csv('matrix.tsv', sep='\t')
bell= read.csv('bell.tsv', sep='\t')
tail= read.csv('tail.tsv', sep='\t')
dfList = list(tail, tsv, bell)
#process csv's
dfList = lapply(dfList, function(dum){
rownames(dum) = dum[,1]
dum[,1] = NULL
dum$X = NULL
dum = dum[, -grep('un', colnames(dum))]
})
#create pca's of dataframes
pcaList = lapply(dfList, function(pca){
prin_comp = prcomp(pca, scale. = T)
})
#plot top 2 principle components in the pca
plotList = lapply(pcaList, function(prin_comp){
t = qplot(x=prin_comp$rotation[,1], y=prin_comp$rotation[,2]) + geom_text_repel(aes(label=row.names(prin_comp$rotation)))
})
#this plots the 3 plots, one for each pca, but they are un-named
plotList
The problem is that the plots don't have meaningful names/titles. I don't know how to keep that information present, passed from function to function.
I know there must be a more elegant way of doing this. And I have spent a day reading similar and not so similar questions regarding processing multiple csv files. But either they weren't applicable or didn't work for my case.
And as the title of this question implies, I would prefer to do this on one csv at a time, not all 3 at a time, as the csv's in question are very large, over 5GB each, so keeping each dataframe and pca in memory at the same time is impossible.

Answer 1

You just need to keep a string you want to use as the title somewhere and add ggtitle(YOUR_TITLE) to your plot, but this is not so easy with your current code. Instead of performing each step of the analysis for each CSV before going to the next step, why don't you just perform all steps for one CSV at a time?
Your code could look like:
library(ggplot2)
library(ggrepel)
csvs <- c("matrix.tsv","bell.tsv","tail.tsv")
for (i in csvs) {
# read file
df <- read.csv(i, sep='\t')
# process file
rownames(df) <- df[,1]
df[,1] <- NULL
df$X = NULL
df = df[, -grep('un', colnames(df))]
# create pca
pca <- prcomp(df, scale = T)
# plot pca
pcaPlot <- qplot(x=pca$rotation[,1], y=pca$rotation[,2]) +
geom_text_repel(aes(label=row.names(pca$rotation))) +
ggtitle(i)
print(pcaPlot)
# extract and plot meaningful variables
# ...
}
Basically I just put everything you do in a lapply call inside of a for loop, this approach also does the processing for one CSV at the time.