I wanted to divide one column by another to get the per person time how can I do this?I couldn't find anything on how you can divide.
Here is some data that I want to use
min / count2.freq
263808.0/1582 = 166.75
There are a plethora of ways in which this can be done. The problem is how to make R aware of the locations of the variables you wish to divide.
d <- read.table(text = "263807.0 1582 196190.5 1016 586689.0 3479 ") names(d) <- c("min", "count2.freq") > d min count2.freq 1 263807.0 1582 2 196190.5 1016 3 586689.0 3479
To add the desired division as a third variable I would use
> d <- transform(d, new = min / count2.freq) > d min count2.freq new 1 263807.0 1582 166.7554 2 196190.5 1016 193.1009 3 586689.0 3479 168.6373
If doing this in a function (i.e. you are programming) then best to avoid the sugar shown above and index. In that case any of these would do what you want
## 1. via `[` and character indexes d[, "new"] <- d[, "min"] / d[, "count2.freq"] ## 2. via `[` with numeric indices d[, 3] <- d[, 1] / d[, 2] ## 3. via `$` d$new <- d$min / d$count2.freq
All of these can be used at the prompt too, but which is easier to read:
d <- transform(d, new = min / count2.freq)
d$new <- d$min / d$count2.freq ## or any of the above examples
Hopefully you think like I do and the first version is better ;-)
The reason we don't use the syntactic sugar of
tranform() et al when programming is because of how they do their evaluation (look for the named variables). At the top level (at the prompt, working interactively)
transform() et al work just fine. But buried in function calls or within a call to one of the
apply() family of functions they can and often do break.
Likewise, be careful using numeric indices (
## 2. above); if you change the ordering of your data, you will select the wrong variables.
If you are just wanting to do the division (rather than insert the result back into the data frame, then use
with(), which allows us to isolate the simple expression you wish to evaluate
> with(d, min / count2.freq)  166.7554 193.1009 168.6373
This is again much cleaner code than the equivalent
> d$min / d$count2.freq  166.7554 193.1009 168.6373
as it explicitly states that "using
d, execute the code
min / count2.freq. Your preference may be different to mine, so I have shown all options.