[R] dplyr - counting a number of specific values in each column - for all columns at once

[Bert Gunter]

... my bad! -- I filed to read carefully.

A base syntax version is:

dat <- data.frame (a=sample(1:5,10,rep=TRUE),
                   b=sample(3:7,10,rep=TRUE),
                   g = sample(7:9,10,rep=TRUE))

dev <- sample(1:3,10,rep=TRUE)

sapply(dat,function(x)
  tapply(x,dev,function(x)sum(x==5,na.rm=TRUE)))

  a b g
1 2 0 0
2 1 3 0
3 2 1 0

I think, no matter what, that there are 2 loops here: An outer one by
column and an inner one by device within each column.

Being both old and lazy, I have found it easier and more natural to stick
with the basic functional syntax of the "apply" family of functions rather
than to learn an alternative database type syntax (and semantics). My
applications were never so large that the possible execution inefficiency
mattered. However, it certainly might for others.  And of course, what is
"natural" for me might not be for others.

Cheers,
Bert

Bert Gunter

"Data is not information. Information is not knowledge. And knowledge is
certainly not wisdom."
   -- Clifford Stoll

On Tue, Jun 16, 2015 at 12:47 PM, Hadley Wickham <h.wickham at gmail.com>
wrote:

> On Tue, Jun 16, 2015 at 12:24 PM, Dimitri Liakhovitski
> <dimitri.liakhovitski at gmail.com> wrote:
> > Hello!
> >
> > I have a data frame:
> >
> > md <- data.frame(a = c(3,5,4,5,3,5), b = c(5,5,5,4,4,1), c =
> c(1,3,4,3,5,5),
> >       device = c(1,1,2,2,3,3))
> > myvars = c("a", "b", "c")
> > md[2,3] <- NA
> > md[4,1] <- NA
> > md
> >
> > I want to count number of 5s in each column - by device. I can do it
> like this:
> >
> > library(dplyr)
> > group_by(md, device) %>%
> > summarise(counts.a = sum(a==5, na.rm = T),
> >           counts.b = sum(b==5, na.rm = T),
> >           counts.c = sum(c==5, na.rm = T))
> >
> > However, in real life I'll have tons of variables (the length of
> > 'myvars' can be very large) - so that I can't specify those counts.a,
> > counts.b, etc. manually - dozens of times.
> >
> > Does dplyr allow to run the count of 5s on all 'myvars' columns at once?
>
> md %>%
>   group_by(device) %>%
>   summarise_each(funs(sum(. == 5, na.rm = TRUE)))
>
> Hadley
>
> --
> http://had.co.nz/
>
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