Interdependencies of variable types, logical expressions and NA

Thu, Apr 28, 2016 12:41 AM

Hi

Your script is not reproducible.

Creating Check_U_0__Kd_1_2011 from Umsatz_2011 and Kunde01_2011
Error in ifelse(Kunden01[[Umsatz]] == 0 & Kunden01[[Kunde]] == 1, 1, 0) :
  object 'Kunden01' not found

This is interesting
x <- c(NA, FALSE, TRUE)
names(x) <- as.character(x)
outer(x, x, "&") ## AND table
       <NA> FALSE  TRUE
<NA>     NA FALSE    NA
FALSE FALSE FALSE FALSE
TRUE     NA FALSE  TRUE

I am not sure, but the logic for AND is to return TRUE only when both expressions are TRUE.

so
T&T = T
F&F = F
T&NA = NA (you cannot decide hence NA)
F&NA = F (you can decide that regardless of NA the result must be F)

outer(x, x, "|") ## OR  table
      <NA> FALSE TRUE
<NA>    NA    NA TRUE
FALSE   NA FALSE TRUE
TRUE  TRUE  TRUE TRUE

OTOH the logic for OR table is that if one of the expressions is TRUE the result must be TRUE
T | T = T
F | F = F
T&NA = T (you can decide that regardless value in NA the result must be T)
F&NA = NA (you cannot decide hence NA)

And I believe that all your results can be explained by this logic.

Cheers
Petr

-----Original Message-----
From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of
G.Maubach at weinwolf.de
Sent: Thursday, April 28, 2016 9:08 AM
To: r-help at r-project.org
Subject: [R] Interdependencies of variable types, logical expressions and NA

Hi All,

my script tries to do the following on factors:

## Check for case 3: Umsatz = 0 & Kunde = 1
for (year in 2011:2015) {

+   Umsatz <- paste0("Umsatz_", year)
+   Kunde <- paste0("Kunde01_", year)
+   Check <- paste0("Check_U_0__Kd_1_", year)
+
+   cat('Creating', Check, 'from', Umsatz, "and", Kunde, '\n')
+
+   Kunden01[[ Check ]] <- ifelse(Kunden01[[ Umsatz ]] == 0 &
+                                 Kunden01[[ Kunde ]] == 1,
+                                 1, 0
+                                 )
+   Kunden01[[ Check ]] <- factor(Kunden01[[ Check ]],
+                                 levels=c(1, 0),
+                                 labels= c("Check 0", "OK")
+                                 )
+
+ }
Creating Check_U_0__Kd_1_2011 from Umsatz_2011 and Kunde01_2011
Creating Check_U_0__Kd_1_2012 from Umsatz_2012 and Kunde01_2012
Creating Check_U_0__Kd_1_2013 from Umsatz_2013 and Kunde01_2013
Creating Check_U_0__Kd_1_2014 from Umsatz_2014 and Kunde01_2014
Creating Check_U_0__Kd_1_2015 from Umsatz_2015 and Kunde01_2015

table(Kunden01$Check_U_0__Kd_1_2011, useNA = "ifany")

Check 0      OK    <NA>
      1      16      13

table(Kunden01$Check_U_0__Kd_1_2012, useNA = "ifany")

Check 0      OK    <NA>
      1      17      12

table(Kunden01$Check_U_0__Kd_1_2013, useNA = "ifany")

Check 0      OK    <NA>
      2      17      13

table(Kunden01$Check_U_0__Kd_1_2014, useNA = "ifany")

Check 0      OK    <NA>
      1      15      14

table(Kunden01$Check_U_0__Kd_1_2015, useNA = "ifany")

Check 0      OK    <NA>
      2      15      13

Kunden01$Check_U_0__Kd_1_all <-

ifelse(Kunden01$Check_U_0__Kd_1_2011 ==
1 |
+                                        Kunden01$Check_U_0__Kd_1_2012 ==
1 |
+                                        Kunden01$Check_U_0__Kd_1_2013 ==
1 |
+                                        Kunden01$Check_U_0__Kd_1_2014 ==
1 |
+                                        Kunden01$Check_U_0__Kd_1_2015 ==
1,
+                                        1, 0)

table(Kunden01$Check_U_0__Kd_1_all, useNA = "ifany")

    0  <NA>
    7    23

(Ann.: I made the values up. But the relations equal real world data.)

I had expected to get back a factor or at least a numeric variable
containing 0, 1 and NA, instead 1 is not included.

I searched the web for information on the treatment of logical expressions
when the data contains NA. I found:

1.
https://stat.ethz.ch/R-manual/R-devel/library/base/html/NA.html
Examples
# Some logical operations do not return NA
c(TRUE, FALSE) & NA
c(TRUE, FALSE) | NA

2.
https://stat.ethz.ch/R-manual/R-devel/library/base/html/Logic.html
NA is a valid logical object. Where a component of x or y is NA, the
result will be NA if the outcome is ambiguous. In other words NA & TRUE
evaluates to NA, but NA & FALSE evaluates to FALSE. See the examples
below.

## construct truth tables :
x <- c(NA, FALSE, TRUE)
names(x) <- as.character(x)
outer(x, x, "&") ## AND table
outer(x, x, "|") ## OR  table
Ann. Not very useful. How should it be read?

3.
http://www.ats.ucla.edu/stat/r/faq/missing.htm
Good explanation for NA in general and in analysis, but no information
about NA in logical expressions.

Then I made some tests with different data types and variables with NA:

-- cut --

# 2016-04-27-001_truth_table_for_logicals_and_NA.R

# Test 1
var2 <- c(TRUE, FALSE)
var3 <- c(NA, NA)
var1 <- c(1, 1)
ds <- data.frame(var1, var2, var3)
ds

ds$value_and_logical <- ifelse(ds$var1 | ds$var2, TRUE, FALSE)
ds$logical_and_na <- ifelse(ds$var2 | ds$var3, TRUE, FALSE)
ds$value_and_na <- ifelse(ds$var1 | ds$var3, TRUE, FALSE)

print(ds)
# Output
# var1  var2 var3 value_and_logical logical_and_na value_and_na
# 1    1  TRUE   NA              TRUE           TRUE         TRUE
# 2    1 FALSE   NA              TRUE             NA         TRUE

# Test 2
ds$var1 <- factor(ds$var1, levels = c(0, 1), labels = c("NOT ok", "OK"))
ds$var2 <- factor(ds$var2, levels = c(0, 1), labels = c("NOT ok", "OK"))
ds$var3 <- factor(ds$var3, levels = c(0, 1), labels = c("NOT ok", "OK"))

ds$value_and_logical <- ifelse(ds$var1 | ds$var2, TRUE, FALSE)
ds$logical_and_na <- ifelse(ds$var2 | ds$var3, TRUE, FALSE)
ds$value_and_na <- ifelse(ds$var1 | ds$var3, TRUE, FALSE)

# Output (abbrev.)
# Warning message:
#  In Ops.factor(ds$var1, ds$var3) : ?|? ist nicht sinnvoll f?r Faktoren

print(ds)
# Output
# var1 var2 var3 value_and_logical logical_and_na value_and_na
# 1   OK <NA> <NA>                NA             NA           NA
# 2   OK <NA> <NA>                NA             NA           NA

-- cut --

I had expected to get the same result in Test 2 as in Test 1.

Where can I find information and documentation about NA handling in
logical expressions on different variable types?

Kind regards

Georg

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Interdependencies of variable types, logical expressions and NA

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