Question

I’m using sqldf to subset an enormous file. The following command gives me a data.frame of 100 rows and 42 columns.

first <- read.csv.sql("first.txt", sep = " ", header = TRUE, row.names = FALSE,
        sql = "SELECT * FROM file WHERE n = '\"n63\"' AND ratio = 1 AND r_name = '\"r1\"' AND method = '\"nearest\"' AND variables = 10")

The structure of the object is

'data.frame':   100 obs. of  42 variables:
 $ test_before       : chr  "TRUE" "TRUE" "TRUE" "TRUE" ...
 $ test_after        : chr  "TRUE" "TRUE" "TRUE" "TRUE" ...
 $ meanPSmatchRATIO  : chr  "1.54845330373635" "1.16857102212364" "1.25330045961256" "1.8011651466717" ...
snipped intervening normally printed columns
 $ PSdiff_DIFF       : chr  "-0.0103938442562762" "-0.00935228868105753" "-0.00947571480267878" 
snipped intervening normally printed columns
 $ nUNMATCHt         : chr  "0" "0" "0" "0" ...
 $ caliper           : chr  "\"no\"" "\"no\"" "\"no\"" "\"no\"" ...
 $ method            : chr  "\"nearest\"" "\"nearest\"" "\"nearest\"" "\"nearest\"" ...
 $ r_name            : chr  "\"r1\"" "\"r1\"" "\"r1\"" "\"r1\"" ...
 $ ratio             : int  1 1 1 1 1 1 1 1 1 1 ...
 $ n                 : chr  "\"n63\"" "\"n63\"" "\"n63\"" "\"n63\"" ...
 $ variables         : int  10 10 10 10 10 10 10 10 10 10 ...

Now, based on this you would expect that when I print the data.frame, all columns (except those int will be character (enclosed in “”)). But you would be wrong!

  test_before test_after meanPSmatchRATIO del-  nUNMATCHt caliper    method r_name ratio     n variables
1        TRUE       TRUE 1.54845330373635 eted          0    "no" "nearest"   "r1"     1 "n63"        10
2        TRUE       TRUE 1.16857102212364 ...           0    "no" "nearest"   "r1"     1 "n63"        10
3        TRUE       TRUE 1.25330045961256 ...           0    "no" "nearest"   "r1"     1 "n63"        10
4        TRUE       TRUE  1.8011651466717 ...t          0    "no" "nearest"   "r1"     1 "n63"        10

Notice that only the last few columns are “character”. I’m a bit lost at what’s going on. Can someone explain?

Answer 1

Looks fine to me. print.data.frame doesn’t usually print quotes for character columns, but those last few columns have embedded quotes, so that’s why they appear “quoted” by default.

Data <- data.frame(x=1:5,y=as.character(1:5),
  z=letters[1:5], q=paste("\"",letters[1:5],"\"",sep=""))
print(Data)  # default print
#   x y z   q
# 1 1 1 a "a"
# 2 2 2 b "b"
# 3 3 3 c "c"
# 4 4 4 d "d"
# 5 5 5 e "e"
print(Data, quote=TRUE)  # show embedded quotes
#     x   y   z       q
# 1 "1" "1" "a" "\"a\""
# 2 "2" "2" "b" "\"b\""
# 3 "3" "3" "c" "\"c\""
# 4 "4" "4" "d" "\"d\""
# 5 "5" "5" "e" "\"e\""