CODEWITHSUNDEEP
rdataframemultiple-columns
Chad
Chad

Reputation: 149

subtract columns in data.frame using conditions in R

What I want to do is subtract columns in data frame if condition is met. This isnt my data, but test data.

x<-mtcars;
x;
                   mpg cyl disp  hp drat   wt  qsec vs am gear carb
Mazda RX4         42.0  12  320 220 7.80 5.24 32.92  0  2    8    8
Mazda RX4 Wag     42.0  12  320 220 7.80 5.75 34.04  0  2    8    8
Datsun 710        45.6   8  216 186 7.70 4.64 37.22  2  2    8    2
Hornet 4 Drive    42.8  12  516 220 6.16 6.43 38.88  2  0    6    2
Hornet Sportabout 37.4  16  720 350 6.30 6.88 34.04  0  0    6    4
Valiant           36.2  12  450 210 5.52 6.92 40.44  2  0    6    2

Below is the code I am trying to use. I want if ncol = carb subtract ncol -2 or if ncol = gear ncol - 1

w <- function(x){if (x[,ncol(x)] == c("carb")) {(ncol(x)-2)} else (ncol(x)-1)};

output:

Warning message:
In if (x[, ncol(x)] == c("carb")) { :
the condition has length > 1 and only the first element will be used

I get that the this is talking about logical things, but I can figure out what the heck to do from here.

I then want to spit this into: (this is for my data, and isnt replicated in data above)

Subtract<- finaltable[paste(tmp), w];

Can someone help me get this to work?

Upvotes: 0

Views: 426

Answers (1)

thelatemail
thelatemail

Reputation: 93813

In light of the comments, you need to use one of either:

names(x)[ncol(x)] # [1] "carb"
tail(names(x),1)  # [1] "carb"

to check against the last column name. As opposed to:

x[,ncol(x)]
#[1] 4 4 1 1 2 1 4 2 2 4 4 3 3 3 4 4 4 1 2 1 1 2 2 4 2 1 2 2 4 6 8 2

...which will actually return the contents of the last column rather than the column name.

Upvotes: 2

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