I have imported a CSV file to R but now I would like to extract a variable into a vector and analyse it separately. Could you please tell me how I could do that?
I know that the summary() function gives a rough idea but I would like to learn more.
I apologise if this is a trivial question but I have watched a number of tutorial videos and have not seen that anywhere.
Read data into data frame using read.csv. Get names of data frame. They should be the names of the CSV columns unless you've done something wrong. Use dollar-notation to get vectors by name. Try reading some tutorials instead of watching videos, then you can try stuff out.
d = read.csv("foo.csv")
names(d)
v = d$whatever # for example
hist(v) # for example
This is totally trivial stuff.
I assume you have use the read.csv() or the read.table() function to import your data in R. (You can have help directly in R with ? e.g. ?read.csv
So normally, you have a data.frame. And if you check the documentation the data.frame is described as a "[...]tightly coupled collections of variables which share many of the properties of matrices and of lists[...]"
So basically you can already handle your data as vector.
A quick research on SO gave back this two posts among others:
And I am sure they are more relevant ones. Try some good tutorials on R (videos are not so formative in this case). There is a ton of good ones on the Internet, e.g: * http://www.introductoryr.co.uk/R_Resources_for_Beginners.html (which lists some) or * http://tryr.codeschool.com/
Anyways, one way to deal with your csv would be:
#import the data to R as a data.frame
mydata = read.csv(file="SomeFile.csv", header = TRUE, sep = ",",
quote = "\"",dec = ".", fill = TRUE, comment.char = "")
#extract a column to a vector
firstColumn = mydata$col1 # extract the column named "col1" of mydata to a vector
#This previous line is equivalent to:
firstColumn = mydata[,"col1"]
#extract a row to a vector
firstline = mydata[1,] #extract the first row of mydata to a vector
Edit: In some cases[1], you might need to coerce the data in a vector by applying functions such as as.numeric or as.character:
firstline=as.numeric(mydata[1,])#extract the first row of mydata to a vector
#Note: the entire row *has to be* numeric or compatible with that class
[1] e.g. it happened to me when I wanted to extract a row of a data.frame inside a nested function
