Syntax question - When to use the letter "c"

[FIC]

I'm unclear on when to use the letter c. I've seen that it's used to mean "combine"
ex. c(1,2,3),

however, can it also mean column?
data[row, c("column name")]

I thought rows and columns can be indicated as data[x,y], without the "c" ?

[Fer]

It does not mean columns, it is showing the same behaviour, to create a vector of columns to be selected

data[row, c("columnname1", "columname2",....)]
data[row, c(1,3:5,7,....)]

And it works the same with rows

data[c(1,4,5:9), c(1,3)]

For selecting rows 1,4,5,6,7,8,9, and columns 1 and 3

You use 'c' to select more than 1 row or columns, by names or position (numbers) with the exception of consecutive ones, like

data[5:9, 2:4]

Where you select rows 5,6,7,8,9 and columns 2,3,4.

[andresrcs]

@FIC

I'm unclear on when to use the letter c

Well it's not a letter, it's a function c() that " Combine Values into a Vector or List", so you need to use the function c() whenever you need to pass a vector or list as a parameter, like in your example

@FIC

data[row, c("column name")]

You are passing a character vector with the names of your columns.

[FIC]

In this case, the "income" column is dropped:

allCols <- colnames(data.test)
drop <- c("Income")
keep <- setdiff(allCols, drop)
keep

In line #2 how do we know this is referring to a column? i'm used to seeing [,column] when referring to a column.

[andresrcs]

@FIC

drop <- c("Income")

This is not referring to a column name per se, it's a character vector of length 1 containing the string "Income", from the context you know that it's also the name of one of the columns.

[Fer]

I am not sure what you want to do with your code, as it i not reproducible, but in line two it is not know to what it is referring (Well, as Andres say, you may know by context, but at that point, R has no idea of what is it, rather than just a vector of length 1 with a string on it). It is just a string It will depend on the context it is used: It can be used to select rows, columns, lists, to subset a data frame.
Think in drop = 5. What is drop? Just a number. You can use to select row number 5, column number 5, the fifth element of a list, to subset a data frame by removing all values larger than 5 etc... drop <-c('Income') has the same behaviour