In R: dcast function, pass column names (again!)

Question

Indication of df in semi-debt format with id aand variables band measured data in m1and columns m2. The data type is set by the variable v(values ​​var1 and var2).

set.seed(8)

df_l <- 
  data.frame(
    a = rep(sample(LETTERS,5),2),
    b = rep(sample(letters,5),2),
    v = c(rep("var1",5),rep("var2",5)),
    m1 = sample(1:10,10,F),
    m2 = sample(20:40,10,F)) 

Looks like:

   a b    v m1 m2
1  W r var1  3 40
2  N l var1  6 32
3  R a var1  9 28
4  F g var1  5 21
5  E u var1  4 38
6  W r var2  1 35
7  N l var2  8 33
8  R a var2 10 29
9  F g var2  7 30
10 E u var2  2 23

If I want to make a wide format of values ​​in m1, using id aas rows and values v1in as columns:

> reshape2::dcast(df_l, a~v, value.var="m1")
  a var1 var2
1 E    4    2
2 F    5    7
3 N    6    8
4 R    9   10
5 W    3    1

How to write a function that does this arguments in dcast(row, column and .var value) are supplied as arguments, for example:

fun <- function(df,row,col,val){
  require(reshape2)
  res <-
    dcast(df, row~col, value.var=val)
  return(res)
}

SO , match.call eval(substitute()) "" , lazyeval . .

? dcast ?

Answer 1

.

foo <- function(df, id, measure, val) {
    dcast(df, paste(paste(id, collapse = " + "), "~", 
                    paste(measure, collapse = " + ")), 
          value.var = val)
}

require(reshape2)
foo(df_l, "a", "v", "m1")

---

, data.table dcast ( ) value.var. , :

require(data.table) # v1.9.5
foo(setDT(df_l), "a", "v", c("m1", "m2"))
#    a m1_var1 m1_var2 m2_var1 m2_var2
# 1: F       1       6      28      21
# 2: H       9       2      38      29
# 3: M       5      10      24      35
# 4: O       8       3      23      26
# 5: T       4       7      31      39