[R] Function on columns of a dataframe

[LogLord]

Hi,

I would like to assign the largest value of a column to a specific category
and repeat this for each column (v1 - v4).

> x=c(1:12)
> cat=c("cat1","cat5","cat2","cat2","cat1","cat5","cat3","cat4","cat5","cat2","cat3","cat6")
> v1=rnorm(12,0.5,0.1)
> v2=rnorm(12,0.3,0.2)
> v3=rnorm(12,0.4,0.1)
> v4=rnorm(12,0.6,0.3)
> bla=data.frame(x,cat,v1,v2,v3,v4)
> bla
    x  cat        v1         v2        v3         v4
1   1 cat1 0.4013144 0.54839317 0.3946393  0.8679266
2   2 cat5 0.4595873 0.45788906 0.4030078  0.5919596
3   3 cat2 0.4542865 0.21516928 0.2777649  0.6112099
4   4 cat2 0.4787950 0.06252512 0.5095611  0.6450795
5   5 cat1 0.4910746 0.56591049 0.5151813  0.8465181
6   6 cat5 0.4194397 0.16592579 0.4361643  0.6415192
7   7 cat3 0.6148564 0.32240342 0.2690108  0.7114133
8   8 cat4 0.6174652 0.28076152 0.4577064 -0.2567284
9   9 cat5 0.4775395 0.28611768 0.4660210  0.4634120
10 10 cat2 0.4802962 0.03715569 0.4506361  1.0063235
11 11 cat3 0.6495094 0.33303172 0.3352933  1.4390324
12 12 cat6 0.4891481 0.45355589 0.3880739  0.7831656
> 

I can assign this by the sqldf() command for each column but I would like to
automate this as I have many columns.

> select=sqldf("select cat, max(v1) FROM bla GROUP BY cat")
> select
   cat   max(v1)
1 cat1 0.4910746
2 cat2 0.4802962
3 cat3 0.6495094
4 cat4 0.6174652
5 cat5 0.4775395
6 cat6 0.4891481
> 

Finally, I would like to have a dataframe where where the cat is followed by
each column maximum.

Thanks for your help!
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