Scatterplot of 2 columns

[Marcos Lancia]

Hi everybody. I have a simple question for bioinformatics. I´d like make a scatterplot of 2 of my columns from a table .csv or .tabular. How can I do that? Thanks!

[Marcos Lancia]

Oh, I'm sorry. I'm working on R. Thanks!

[blancha]

library(data.table)

# Read data with fread.
# You could also use read.table or read.csv, but fread has many advantages.
data <- data.table::fread("test.csv")

# Basic scatter plot.
plot(data$V1, data$V2)

library(ggplot2)

# A slightly different scatter plot with ggplot2
# Very easy to generate prettier plots with ggplot2. 
# Takes time to understand underlying concepts though.
ggplot2::qplot(data$V1, data$V2)

[dpryan]

d <- read.csv("some_file.csv", header=T) #Presuming there's a header
plot(d[,1], d[,2]) # or plot(d$FirstColumnLabel, d$SecondColumnLabel)

Edit: I guess I should have refreshed, Blancha beat me to it.

[blancha]

@dpryan
That's fine.
Your answer does raise a good point for a novice R user.

@Marcos Lancia If your csv file does have column headers, you should use those instead of V1 and V2, which are the default column headers generated by fread.
There are several other subtleties, even for this question, which is just about the most basic question one can ask in R.
That's why I've stopped trying to teach R to wet-lab biologists.
I like fread, because it is extremely fast, and can detect several other features of the files, such as the column separator, or the presence or absence of column headers, which often have to be explicitly specified with read.csv.
However, fread returns a data.table by default, not a data.frame, which is a slightly different data structure.
If you'd like to get a more traditional data.frame, you just have to specify data.table = FALSE.

 fread("test.csv", data.table=FALSE)

With a data.table, you can't specify the column index in exactly the format given by @dpryan. You can specify the column by the column label in the same manner, though.
To get the first column by index of a data.table, you need to use the following format.

data[, 1, with=FALSE]

Hopefully, you're not now completely lost.
You'll understand why I've stopped given workshops in R. D)

@dpryan's answer is more direct. read.csv() and plot()

[Marcos Lancia]

Hi people, thanks for writing. I'll check it out your ideas, I'll see how well I understand your commands.

[Marcos Lancia]

I´m working with dpryan's commands. I could make variable d, but when I tried plotting

plot(d$log2(FC transcriptome), d$log2(FC translatome))

but there's an error message saying
Error: unexpected symbol in "plot(d$log2(FC transcriptome"

What can I do?
Thanks!

[Marcos Lancia]

little advances

"log2(FC transcriptome)", and "log2(FC translatome)" are my headers that I want to plot. They´re the 10th and 24th columns in my table.

[blancha]

Yes, that's not going to work.

You can't have space in a R variable name.
As always, there is a work-around.
You can put the variable names in back ticks: `FC transcriptome`is acceptable.
You need to call log2 on the column too.
log2(d$`FC transcriptome`)

The function read.csv must have replaced the blank spaces by periods anyway.

So, the correct code would be.

 plot(log2(d$FC.transcriptome), log2(d$FC.translatome))

You should check the head of the data frame, to be sure that you have the correct column names, and that the file was read correctly.

head(d)
colnames(d)

EDIT for update
If the colunm name in your file is log2(FC transcriptome), read.csv will convert the column name to log2.FC.transcriptome.
Just check the colnames and the header of the data frame with the commands posted above.

[Marcos Lancia]

I tried the same with ggplot, and the answer was the same.

[blancha]

Just want to point out that with RStudio you can import a file by just clicking on "Import Dataset", and also just view the data frame by clicking on the name of the data frame.

Highly recommend RStudio for both novices and power users.

Edit for update
Just post the output of the following command, so that we know the format of your data frame.

head(d)

[blancha]

Or, since you said that it is the 10th and 24th columns, you could just specify the columns by the index number.

plot(d[,10], d[,24])

One should always check the format of the data frame first after reading a CSV file, though.

[Marcos Lancia]

Ok! you're right. I changed the names of the headers, but I crashed with a new problem. I have some non-numerical data in the columns, some are "inf" or "-inf". How can I avoid that?

[Marcos Lancia]

I tried before with plot(d[,10], d[,24]), but it says "error in evaluating the argument 'x' in selecting a method for function 'plot': Error in `[.data.frame`(d, , 10) : undefined columns selected"

> head(d)
test_id.gene_id.gene.locus.sample_1.sample_2.status.value_1.value_2.log2.FC.transcriptome..test_stat.p_value.q_value.significant.test_id.gene_id.gene.locus.sample_1.sample_2.status.value_1.value_2.log2.FC.translatome..test_stat.p_value.q_value.significant
1 TCONS_00000001\tXLOC_000001\tMedtr1g004940\tchr1:688-7366\tSN16 mock\tSN16 Sm\tNOTEST\t0\t0\t0\t0\t1\t1\tno\tTCONS_00000001\tXLOC_000001\tMedtr1g004940\tchr1:688-7366\tTRAP mock\tTRAP Sm\tNOTEST\t0\t0\t0\t0\t1\t1\tno
2 TCONS_00000002\tXLOC_000002\tMedtr1g004950\tchr1:14513-15729\tSN16 mock\tSN16 Sm\tNOTEST\t0\t0\t0\t0\t1\t1\tno\tTCONS_00000002\tXLOC_000002\tMedtr1g004950\tchr1:14513-15729\tTRAP mock\tTRAP Sm\tNOTEST\t0\t0\t0\t0\t1\t1\tno
3 TCONS_00000003\tXLOC_000003\tMedtr1g004960\tchr1:16282-18382\tSN16 mock\tSN16 Sm\tNOTEST\t0\t0\t0\t0\t1\t1\tno\tTCONS_00000003\tXLOC_000003\tMedtr1g004960\tchr1:16282-18382\tTRAP mock\tTRAP Sm\tNOTEST\t0\t0\t0\t0\t1\t1\tno
4 TCONS_00000004\tXLOC_000004\tMedtr1g004980\tchr1:31972-32344\tSN16 mock\tSN16 Sm\tNOTEST\t0\t0\t0\t0\t1\t1\tno\tTCONS_00000004\tXLOC_000004\tMedtr1g004980\tchr1:31972-32344\tTRAP mock\tTRAP Sm\tNOTEST\t0\t0\t0\t0\t1\t1\tno
5 TCONS_00000005\tXLOC_000005\tMedtr1g004990\tchr1:35909-40554\tSN16 mock\tSN16 Sm\tNOTEST\t0
6 203657\t0

[blancha]

The default line separator for read.csv is the comma.
If your file is tab-delimited, it will not separate the columns by tab.

Choice #1: Use read.csv, and specify the separator. Not my favorite solution, but most commonly used.

d <- read.csv("test.csv", sep="\t")

Choice #2: Much better in my opinion. Install dtable, and use the fread function.
fread automatically picks up the column separator

install.packages("data.table")
library(data.table) 
d <- fread("test.csv", data.table=FALSE)

Choice #3
Use the Import Dataset button in RStudio.
Specify the column separator in pop-up menu.
Quick solution for R novices.