fread parse Y/N as bool (#4564)

* basic idea for Y/N bool parser * New logicalYN argument * NEWS * tests * missing \arguments{} entry * Some comments --------- Co-authored-by: Michael Chirico <michael.chirico@grabtaxi.com>
Rdatatable · Dec 9, 2024 · 436bd6c · 436bd6c
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diff --git a/NEWS.md b/NEWS.md
@@ -67,6 +67,8 @@ rowwiseDT(
 
 5. `setcolorder()` gains `skip_absent` to ignore unrecognized columns (i.e. columns included in `neworder` but not present in the data), [#6044,  #6068](https://github.com/Rdatatable/data.table/pull/6044). Default behavior (`skip_absent=FALSE`) remains unchanged, i.e. unrecognized columns result in an error. Thanks to @sluga for the suggestion and @sluga & @Nj221102 for the PRs.
 
+6. `fread()` gains `logicalYN` argument to read columns consisting only of strings `Y`, `N` as `logical` (as opposed to character), [#4563](https://github.com/Rdatatable/data.table/issues/4563). The default is controlled by option `datatable.logicalYN`, itself defaulting to `FALSE`, for back-compatibility -- some smaller tables (especially sharded tables) might inadvertently read a "true" string column as `logical` and cause bugs. This is particularly important for tables with a column named `y` or `n` -- automatic header detection under `logicalYN=TRUE` will see these values in the first row as being "data" as opposed to column names. A parallel option was not included for `fwrite()` at this time -- users looking for a compact representation of logical columns can still use `fwrite(logical01=TRUE)`. We also opted for now to check only `Y`, `N` and not `Yes`/`No`/`YES`/`NO`.
+
 ## BUG FIXES
 
 1. `fwrite()` respects `dec=','` for timestamp columns (`POSIXct` or `nanotime`) with sub-second accuracy, [#6446](https://github.com/Rdatatable/data.table/issues/6446). Thanks @kav2k for pointing out the inconsistency and @MichaelChirico for the PR.

diff --git a/R/fread.R b/R/fread.R
@@ -4,7 +4,9 @@ na.strings=getOption("datatable.na.strings","NA"), stringsAsFactors=FALSE, verbo
 skip="__auto__", select=NULL, drop=NULL, colClasses=NULL, integer64=getOption("datatable.integer64","integer64"),
 col.names, check.names=FALSE, encoding="unknown", strip.white=TRUE, fill=FALSE, blank.lines.skip=FALSE, key=NULL, index=NULL,
 showProgress=getOption("datatable.showProgress",interactive()), data.table=getOption("datatable.fread.datatable",TRUE),
-nThread=getDTthreads(verbose), logical01=getOption("datatable.logical01",FALSE), keepLeadingZeros=getOption("datatable.keepLeadingZeros",FALSE),
+nThread=getDTthreads(verbose), logical01=getOption("datatable.logical01",FALSE),
+logicalYN=getOption("datatable.logicalYN", FALSE),
+keepLeadingZeros=getOption("datatable.keepLeadingZeros",FALSE),
 yaml=FALSE, autostart=NA, tmpdir=tempdir(), tz="UTC")
 {
   if (missing(input)+is.null(file)+is.null(text)+is.null(cmd) < 3L) stopf("Used more than one of the arguments input=, file=, text= and cmd=.")
@@ -24,7 +26,7 @@ yaml=FALSE, autostart=NA, tmpdir=tempdir(), tz="UTC")
   }
   stopifnot(
     isTRUEorFALSE(strip.white), isTRUEorFALSE(blank.lines.skip), isTRUEorFALSE(fill) || is.numeric(fill) && length(fill)==1L && fill >= 0L, isTRUEorFALSE(showProgress),
-    isTRUEorFALSE(verbose), isTRUEorFALSE(check.names), isTRUEorFALSE(logical01), isTRUEorFALSE(keepLeadingZeros), isTRUEorFALSE(yaml),
+    isTRUEorFALSE(verbose), isTRUEorFALSE(check.names), isTRUEorFALSE(logical01), isTRUEorFALSE(logicalYN), isTRUEorFALSE(keepLeadingZeros), isTRUEorFALSE(yaml),
     isTRUEorFALSE(stringsAsFactors) || (is.double(stringsAsFactors) && length(stringsAsFactors)==1L && 0.0<=stringsAsFactors && stringsAsFactors<=1.0),
     is.numeric(nrows), length(nrows)==1L
   )
@@ -277,7 +279,7 @@ yaml=FALSE, autostart=NA, tmpdir=tempdir(), tz="UTC")
       tz="UTC"
   }
   ans = .Call(CfreadR,input,identical(input,file),sep,dec,quote,header,nrows,skip,na.strings,strip.white,blank.lines.skip,
-              fill,showProgress,nThread,verbose,warnings2errors,logical01,select,drop,colClasses,integer64,encoding,keepLeadingZeros,tz=="UTC")
+              fill,showProgress,nThread,verbose,warnings2errors,logical01,logicalYN,select,drop,colClasses,integer64,encoding,keepLeadingZeros,tz=="UTC")
   if (!length(ans)) return(null.data.table())  # test 1743.308 drops all columns
   nr = length(ans[[1L]])
   require_bit64_if_needed(ans)

diff --git a/inst/tests/tests.Rraw b/inst/tests/tests.Rraw
@@ -5567,6 +5567,10 @@ test(1343.5, fread("A,B\n1,true\n2,\n3,false"), data.table(A=1:3, B=c(TRUE,NA,FA
 test(1343.6, fread("A,B\n1,true\n2,NA\n3,"), data.table(A=1:3, B=c(TRUE,NA,NA)))
 test(1344.1, fread("A,B\n1,2\n0,3\n,1\n", logical01=FALSE), data.table(A=c(1L,0L,NA),      B=c(2L,3L,1L)))
 test(1344.2, fread("A,B\n1,2\n0,3\n,1\n", logical01=TRUE),  data.table(A=c(TRUE,FALSE,NA), B=c(2L,3L,1L)))
+test(1344.3, fread("A,B\nY,2\nN,3\nNA,1\n", logicalYN=FALSE), data.table(A=c('Y','N',NA),    B=c(2L,3L,1L)))
+test(1344.4, fread("A,B\nY,2\nN,3\nNA,1\n", logicalYN=TRUE),  data.table(A=c(TRUE,FALSE,NA), B=c(2L,3L,1L)))
+test(1344.5, fread("A,B\nY,2\nN,3\n,1\n", logicalYN=FALSE, na.strings=""), data.table(A=c('Y','N',NA),    B=c(2L,3L,1L)))
+test(1344.6, fread("A,B\nY,2\nN,3\n,1\n", logicalYN=TRUE, na.strings=""),  data.table(A=c(TRUE,FALSE,NA), B=c(2L,3L,1L)))
 
 # .N now available in i
 DT = data.table(a=1:3,b=1:6)
@@ -7870,9 +7874,14 @@ str = "a,b\n1.5,\"at the 5\" end of the gene.\""
 test(1551.1, fread(str), data.table(a = 1.5, b = "at the 5\" end of the gene."), warning=w<-"resolved improper quoting")
 #1256
 str = "x,y\nx1,\"oops\" y1\n"
-test(1551.2, fread(str), data.table(x = "x1", y = "\"oops\" y1"), warning=w)
+test(1551.21, fread(str), data.table(x='x1', y='"oops" y1'), warning=w)
+# during header detection, 'y' is seen as a valid value --> header determined 'FALSE' despite later non-Y/N data
+test(1551.22, fread(str, logicalYN=TRUE), data.table(V1=c('x', 'x1'), V2=c('y', '"oops" y1')), warning=w)
+test(1551.23, fread(str, logicalYN=TRUE, header=TRUE), data.table(x='x1', y='"oops" y1'), warning=w)
 str = "x,y\nx1,\"oops\" y1"
-test(1551.3, fread(str), data.table(x = "x1", y = "\"oops\" y1"), warning=w)
+test(1551.31, fread(str), data.table(x="x1", y='"oops" y1'), warning=w)
+test(1551.32, fread(str, logicalYN=TRUE), data.table(V1=c('x', 'x1'), V2=c('y', '"oops" y1')), warning=w)
+test(1551.33, fread(str, logicalYN=TRUE, header=TRUE), data.table(x="x1", y='"oops" y1'), warning=w)
 #1077
 str = '2,3\n""foo,bar'
 test(1551.4, fread(str), data.table(V1=c("2","\"\"foo"), V2=c("3","bar")), warning=w)
@@ -7882,8 +7891,12 @@ test(1551.5, fread(str),
   data.table(L1 = c("L2", "L3"), some = c("some", "this"), unquoted = c("\"half\" quoted", "should work"), stuff = c("stuff", "ok though")),
   warning = w)
 #1095
-rhs = read.table(testDir("issue_1095_fread.txt.bz2"), sep=",", comment.char="", stringsAsFactors=FALSE, quote="", strip.white=TRUE)
-if (test_R.utils) test(1551.6, fread(testDir("issue_1095_fread.txt.bz2"), logical01=FALSE), setDT(rhs), warning=w)
+rhs = setDT(read.table(testDir("issue_1095_fread.txt.bz2"), sep=",", comment.char="", stringsAsFactors=FALSE, quote="", strip.white=TRUE))
+if (test_R.utils) {
+  test(1551.61, fread(testDir("issue_1095_fread.txt.bz2"), logical01=FALSE), rhs, warning=w)
+  rhs[, names(.SD) := lapply(.SD, \(x) x == "Y"), .SDcols = c("V16", "V17", "V45")]
+  test(1551.62, fread(testDir("issue_1095_fread.txt.bz2"), logical01=FALSE, logicalYN=TRUE), rhs, warning=w)
+}
 
 # FR #1314 rest of na.strings issue
 str = "a,b,c,d\n#N/A,+1,5.5,FALSE\n#N/A,5,6.6,TRUE\n#N/A,+1,#N/A,-999\n#N/A,#N/A,-999,FALSE\n#N/A,1,NA,TRUE"
@@ -7896,8 +7909,10 @@ test(1552.3, fread(str, na.strings=c("#N/A", "-999", "+1")), read_table(str, na.
 test(1552.4, fread(str, na.strings=c("#N/A", "-999", "+1", "1")), read_table(str, na.strings=c("#N/A", "-999", "+1", "1"))) # enabled by FR #2927
 test(1552.5, fread(str, na.strings=c("#N/A", "-999", "FALSE")), error="NAstring <<FALSE>>.*boolean.*not permitted")
 test(1552.6, fread("A\n1.0\n2\n-", na.strings=c("-")), data.table(A=c(1.0, 2.0, NA)))
-test(1552.7, fread(str, na.strings=c("#N/A", "-999", "+1", "1"), logical01=TRUE),
+test(1552.71, fread(str, na.strings=c("#N/A", "-999", "+1", "1"), logical01=TRUE),
   error="NAstring <<1>> and logical01=TRUE.*not permitted")
+test(1552.72, fread(str, na.strings=c("#N/A", "-999", "+1", "Y"), logicalYN=TRUE),
+  error="NAstring <<Y>> and logicalYN=TRUE.*not permitted")
 str = "a,b,c\n0,1,2\n1,0,2"
 test(1552.8, fread(str, na.strings = "0"), data.table(a=c(NA,1L), b=c(1L,NA), c=c(2L,2L)))
 test(1552.9, fread(str, na.strings = c("0","1")), data.table(a=c(NA,NA), b=c(NA,NA), c=c(2L,2L)))
@@ -8896,8 +8911,10 @@ test(1618.5, fread("a,c,b\n1,2,3", select=c("b", "c"), col.names=c("q", "r")), d
 test(1618.6, fread("a,c,b\n1,2,3", select=c("b", "z")), data.table(b=3L), warning="Column name 'z' not found.*skipping")
 
 # Additional test for 1445 for non-monotonic integer select
-select1618.8 <- c(4, 9, 8, 23, 1, 21, 5, 18, 11, 13)
-test(1618.8, names(fread("a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z\na,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z", select = select1618.8)), letters[select1618.8])
+select1618 <- c(4, 9, 8, 23, 1, 21, 5, 18, 11, 13)
+str = paste0(paste(letters, collapse=','), '\n', paste(letters, collapse=','))
+test(1618.8, names(fread(str, select=select1618)), letters[select1618])
+test(1618.9, names(fread(str, select=select1618, logicalYN=TRUE)), paste0('V', select1618))
 
 # fix for #1270. Have been problems with R before vs after 3.1.0 here. But now ok in all R versions.
 DT = data.table(x=1:2, y=5:6)
@@ -9106,7 +9123,8 @@ test(1626.91, fsetdiff(DT, DT["b"]), DT[c(1,4)])
 # fix for #1087 and #1465
 test(1627.1, charToRaw(names(fread(testDir("issue_1087_utf8_bom.csv")))[1L]), as.raw(97L))
 test(1627.2, names(fread(testDir("issue_1087_utf8_bom.csv"), verbose=TRUE))[1L], "a", output="UTF-8 byte order mark EF BB BF found")
-test(1627.3, names(fread(testDir("gb18030.txt")))[1L], "x", warning="GB-18030 encoding detected")
+test(1627.31, names(fread(testDir("gb18030.txt")))[1L], "x", warning="GB-18030 encoding detected")
+test(1627.32, names(fread(testDir("gb18030.txt"), logicalYN=TRUE))[1L], "V1", warning="GB-18030 encoding detected")
 test(1627.4, fread(testDir("utf16le.txt")), error="File is encoded in UTF-16")
 test(1627.5, fread(testDir("utf16be.txt")), error="File is encoded in UTF-16")
 
@@ -11448,9 +11466,11 @@ unlink(f)
 test(1753.1, fread("X,Y\n1,2\n3,4\n5,6"), data.table(X=INT(1,3,5),Y=INT(2,4,6)))
 test(1753.2, fread("X,Y\n1,2\n3,4,\n5,6",logical01=TRUE), ans<-data.table(X=TRUE,Y=2L), warning="Stopped.*line 3. Expected 2 fields but found 3.*discarded.*<<3,4,>>")
 test(1753.3, fread("X,Y\n1,2\n3,4,7\n5,6",logical01=TRUE), ans,                         warning="Stopped.*line 3. Expected 2 fields but found 3.*discarded.*<<3,4,7>>")
+test(1753.4, fread("X,Y\nY,2\n3,4,\n5,6",logicalYN=TRUE), ans<-data.table(X=TRUE,Y=2L), warning="Stopped.*line 3. Expected 2 fields but found 3.*discarded.*<<3,4,>>")
+test(1753.5, fread("X,Y\nY,2\n3,4,7\n5,6",logicalYN=TRUE), ans,                         warning="Stopped.*line 3. Expected 2 fields but found 3.*discarded.*<<3,4,7>>")
 
 # issue 2051 where a quoted field contains ",  New quote rule detection handles it.
-if (test_R.utils) test(1753.4, fread(testDir("issue_2051.csv.gz"))[2,grep("^Our.*tool$",COLUMN50)], 1L)
+if (test_R.utils) test(1753.6, fread(testDir("issue_2051.csv.gz"))[2,grep("^Our.*tool$",COLUMN50)], 1L)
 
 # check omp critical around SET_STRING_ELT
 # minimal construction big enough for parallelism with 8 or less threads. On a machine with more, do setDTthreads(8) first otherwise

diff --git a/man/fread.Rd b/man/fread.Rd
@@ -23,6 +23,7 @@ showProgress=getOption("datatable.showProgress", interactive()),
 data.table=getOption("datatable.fread.datatable", TRUE),
 nThread=getDTthreads(verbose),
 logical01=getOption("datatable.logical01", FALSE),  # due to change to TRUE; see NEWS
+logicalYN=getOption("datatable.logicalYN", FALSE),
 keepLeadingZeros = getOption("datatable.keepLeadingZeros", FALSE),
 yaml=FALSE, autostart=NA, tmpdir=tempdir(), tz="UTC"
 )
@@ -61,6 +62,7 @@ yaml=FALSE, autostart=NA, tmpdir=tempdir(), tz="UTC"
   \item{data.table}{ TRUE returns a \code{data.table}. FALSE returns a \code{data.frame}. The default for this argument can be changed with \code{options(datatable.fread.datatable=FALSE)}.}
   \item{nThread}{The number of threads to use. Experiment to see what works best for your data on your hardware.}
   \item{logical01}{If TRUE a column containing only 0s and 1s will be read as logical, otherwise as integer.}
+  \item{logicalYN}{If TRUE a column containing only Ys and Ns will be read as logical, otherwise as character.}
   \item{keepLeadingZeros}{If TRUE a column containing numeric data with leading zeros will be read as character, otherwise leading zeros will be removed and converted to numeric.}
   \item{yaml}{ If \code{TRUE}, \code{fread} will attempt to parse (using \code{\link[yaml]{yaml.load}}) the top of the input as YAML, and further to glean parameters relevant to improving the performance of \code{fread} on the data itself. The entire YAML section is returned as parsed into a \code{list} in the \code{yaml_metadata} attribute. See \code{Details}. }
   \item{autostart}{ Deprecated and ignored with warning. Please use \code{skip} instead. }

diff --git a/src/data.table.h b/src/data.table.h
@@ -294,7 +294,7 @@ SEXP setcharvec(SEXP, SEXP, SEXP);
 SEXP chmatch_R(SEXP, SEXP, SEXP);
 SEXP chmatchdup_R(SEXP, SEXP, SEXP);
 SEXP chin_R(SEXP, SEXP);
-SEXP freadR(SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP);
+SEXP freadR(SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP);
 SEXP fwriteR(SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP);
 SEXP rbindlist(SEXP, SEXP, SEXP, SEXP, SEXP);
 SEXP setlistelt(SEXP, SEXP, SEXP);

diff --git a/src/fread.c b/src/fread.c
@@ -75,8 +75,9 @@ static freadMainArgs args = {0};  // global for use by DTPRINT; static implies =
   static int mmp_fd = -1;
 #endif
 
-const char typeName[NUMTYPE][10] = {"drop", "bool8", "bool8", "bool8", "bool8", "bool8", "int32", "int64", "float64", "float64", "float64", "int32", "float64", "string"};
-int8_t     typeSize[NUMTYPE]     = { 0,      1,       1,       1,       1,       1,       4,       8,       8,         8,         8,         4,       8       ,  8      };
+// See header for more explanation.
+const char typeName[NUMTYPE][10] = {"drop", "bool8", "bool8", "bool8", "bool8", "bool8", "bool8", "int32", "int64", "float64", "float64", "float64", "int32", "float64", "string"};
+int8_t     typeSize[NUMTYPE]     = { 0,      1,       1,       1,       1,       1,      1,       4,       8,       8,         8,         8,         4,       8       ,  8      };
 
 // In AIX, NAN and INFINITY don't qualify as constant literals. Refer: PR #3043
 // So we assign them through below init function.
@@ -1154,6 +1155,21 @@ static void parse_bool_lowercase(FieldParseContext *ctx)
   }
 }
 
+/* Parse Y | y | N | n as boolean */
+static void parse_bool_yesno(FieldParseContext *ctx)
+{
+  const char *ch = *(ctx->ch);
+  int8_t *target = (int8_t*) ctx->targets[sizeof(int8_t)];
+  if (ch[0] == 'Y' || ch[0] == 'y') {
+    *target = 1;
+    *(ctx->ch) = ch + 1;
+  } else if (ch[0] == 'N' || ch[0] == 'n') {
+    *target = 0;
+    *(ctx->ch) = ch + 1;
+  } else {
+    *target = NA_BOOL8;
+  }
+}
 
 /* How to register a new parser
  *  (1) Write the parser
@@ -1170,6 +1186,7 @@ static reader_fun_t fun[NUMTYPE] = {
   (reader_fun_t) &parse_bool_uppercase,
   (reader_fun_t) &parse_bool_titlecase,
   (reader_fun_t) &parse_bool_lowercase,
+  (reader_fun_t) &parse_bool_yesno,
   (reader_fun_t) &StrtoI32,
   (reader_fun_t) &StrtoI64,
   (reader_fun_t) &parse_double_regular,
@@ -1326,7 +1343,9 @@ int freadMain(freadMainArgs _args) {
           strcmp(ch,"True")==0 || strcmp(ch,"False")==0)
         STOP(_("freadMain: NAstring <<%s>> is recognized as type boolean, this is not permitted."), ch);
       if ((strcmp(ch,"1")==0 || strcmp(ch,"0")==0) && args.logical01)
-        STOP(_("freadMain: NAstring <<%s>> and logical01=TRUE, this is not permitted."), ch);
+        STOP(_("freadMain: NAstring <<%s>> and %s=TRUE, this is not permitted."), ch, "logical01");
+      if ((strcmp(ch,"Y")==0 || strcmp(ch,"N")==0) && args.logicalYN)
+        STOP(_("freadMain: NAstring <<%s>> and %s=TRUE, this is not permitted."), ch, "logicalYN");
       char *end;
       errno = 0;
       (void)strtod(ch, &end);  // careful not to let "" get to here as strtod considers "" numeric
@@ -1335,6 +1354,7 @@ int freadMain(freadMainArgs _args) {
     nastr++;
   }
   disabled_parsers[CT_BOOL8_N] = !args.logical01;
+  disabled_parsers[CT_BOOL8_Y] = !args.logicalYN;
   disabled_parsers[CT_ISO8601_DATE] = disabled_parsers[CT_ISO8601_TIME] = args.oldNoDateTime; // temporary new option in v1.13.0; see NEWS
   if (verbose) {
     if (*NAstrings == NULL) {
@@ -1353,6 +1373,7 @@ int freadMain(freadMainArgs _args) {
     if (args.skipString) DTPRINT(_("  skip to string = <<%s>>\n"), args.skipString);
     DTPRINT(_("  show progress = %d\n"), args.showProgress);
     DTPRINT(_("  0/1 column will be read as %s\n"), args.logical01? "boolean" : "integer");
+    DTPRINT(_("  Y/N column will be read as %s\n"), args.logicalYN? "boolean" : "character");
   }
   if (*NAstrings==NULL ||                             // user sets na.strings=NULL
       (**NAstrings=='\0' && *(NAstrings+1)==NULL)) {  // user sets na.strings=""

diff --git a/src/fread.h b/src/fread.h
@@ -17,6 +17,12 @@
 #endif
 
 // Ordered hierarchy of types
+// Each of these corresponds to a parser; they must be ordered "preferentially", i.e., if the same
+//   input could be validly parsed as both types t1 and t2, and we "prefer" type t1, t1 must come
+//   before t2. Most commonly, we prefer types using less storage. For example, characters '1.34'
+//   in a file could be double, complex, or string. We prefer double, which uses only 8 bytes.
+//   Similarly, '1234' could be integer, double, integer64, complex, or string. We prefer integer,
+//   which uses only 4 bytes.
 typedef enum {
   NEG = -1,        // dummy to force signed type; sign bit used for out-of-sample type bump management
   CT_DROP = 0,     // skip column requested by user; it is navigated as a string column with the prevailing quoteRule
@@ -25,6 +31,7 @@ typedef enum {
   CT_BOOL8_U,
   CT_BOOL8_T,
   CT_BOOL8_L,
+  CT_BOOL8_Y,      // Y/N-as-bool
   CT_INT32,        // int32_t
   CT_INT64,        // int64_t
   CT_FLOAT64,      // double (64-bit IEEE 754 float)
@@ -38,8 +45,10 @@ typedef enum {
 
 #define IS_DEC_TYPE(x) ((x) == CT_FLOAT64 || (x) == CT_FLOAT64_EXT || (x) == CT_ISO8601_TIME) // types where dec matters
 
-extern int8_t typeSize[NUMTYPE];
+// Used to govern when coercion is allowed. We cannot coerce to a "lower" type, unless it has the same typeName.
 extern const char typeName[NUMTYPE][10];
+extern int8_t typeSize[NUMTYPE];
+
 extern const long double pow10lookup[301];
 extern const uint8_t hexdigits[256];
 
@@ -149,6 +158,10 @@ typedef struct freadMainArgs
   // will become integer.
   bool logical01;
 
+  // If true, then column of Ns and Ys will be read as logical, otherwise it
+  // will become character.
+  bool logicalYN;
+
   bool keepLeadingZeros;
 
   // should datetime with no Z or UTZ-offset be read as UTC?