OT: Your signature [Bioanalytics]

posted by Helmut Homepage – Vienna, Austria, 2019-03-27 13:41 (662 d 14:16 ago) – Posting: # 20093
Views: 3,763

Hi ElMaestro,

x=c("Foo", "Bar")
typeof(b[,1]) ##aha, integer?
b[,1]+1 ##then let me add 1

[image]Lemme explain:

x <- c("Foo", "Bar")
[1] TRUE
b <- data.frame(x)
[1] TRUE
1 Foo
2 Bar

  So far, so good. What else?
'data.frame':   2 obs. of  1 variable:
 $ x:
Factor w/ 2 levels "Bar","Foo": 2 1

  Implicitly you are using the default of data.frame() like here:
c <- data.frame(x, stringsAsFactors=TRUE)
  Check #1
identical(c, b)
[1] TRUE

  Check #2
c == b
[1,] TRUE
[2,] TRUE

  See the point?
typeof(b[, 1]) ##aha, integer?
[1] "integer"

  Correct. Factors are always coded as integers internally.
  Check #3
is.factor(b[, 1])
[1] TRUE

  Note also the output of str(b) above where factors are given in lexical order.
  However, since we defined x <- c("Foo", "Bar"), "Bar" gets the level 2
  and "Foo" the level 1 in b.
b[, 1]+1 ##then let me add 1
[1] NA NA
Warning message:
In Ops.factor(b[, 1], 1) : ‘+’ not meaningful for factors

  Well roared, lion!
  On the other hand:
d <- data.frame(x, stringsAsFactors=FALSE)
1 Foo
2 Bar

'data.frame':   2 obs. of  1 variable:
 $ x:
chr  "Foo" "Bar"
typeof(c[, 1])
[1] "character"

  Is this what you expected?
d[, 1]+1
Error in c[, 1] + 1 : non-numeric argument to binary operator

  Sure. Rubbish in, rubbish out.
  Personally I prefer a straight error over a warning producing NAs.


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Helmut Schütz

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