Reset gap counter for each column

Calling na.locf() on a multi-column xts object that is all NA except
for the first row did not carry the first row value forward. This was
caused by maxgap = nrow(x) and the gap counter not being reset after
looping over the first column. This would have also been a problem if
all but the last row were NA and na.locf() was called with fromLast =
FALSE.

Fixes #232.

inst/unitTests/runit.na.locf.R

@@ -158,3 +158,33 @@ test.nalocf_by_column_xout <- function() {
     checkEquals(x, as.xts(z), check.attributes = TRUE)
   }
 }
+
+test.nalocf_by_column_1NA <- function() {
+  narow <- 1L
+  for (m in MODES) {
+    xdrow <- XDAT2[narow,]
+    xdat <- XDAT2 * NA
+    xdat[narow,] <- xdrow
+    storage.mode(xdat) <- m
+    zdat <- as.zoo(xdat)
+
+    x <- na.locf(xdat)
+    z <- na.locf(zdat)
+    checkEquals(x, as.xts(z), check.attributes = TRUE)
+  }
+}
+
+test.nalocf_by_column_1NA_fromLast <- function() {
+  narow <- nrow(XDAT2)
+  for (m in MODES) {
+    xdrow <- XDAT2[narow,]
+    xdat <- XDAT2 * NA
+    xdat[narow,] <- xdrow
+    storage.mode(xdat) <- m
+    zdat <- as.zoo(xdat)
+
+    x <- na.locf(xdat, fromLast = TRUE)
+    z <- na.locf(zdat, fromLast = TRUE)
+    checkEquals(x, as.xts(z), check.attributes = TRUE)
+  }
+}

src/na.c

@@ -175,6 +175,7 @@ SEXP na_locf (SEXP x, SEXP fromLast, SEXP _maxgap, SEXP _limit)
             int_result[i] = int_x[i];
           }
           /* result[_first] now has first value fromLast=FALSE */
+          gap = 0;
           for(i=_first+1; i<nr+j*nr; i++) {
             int_result[i] = int_x[i];
             if(int_result[i] == NA_LOGICAL && gap < maxgap) {
@@ -192,6 +193,7 @@ SEXP na_locf (SEXP x, SEXP fromLast, SEXP _maxgap, SEXP _limit)
         /* nr-2 is first position to fill fromLast=TRUE */
         for(j=0; j < nc; j++) {
           int_result[nr-1+j*nr] = int_x[nr-1+j*nr];
+          gap = 0;
           for(i=nr-2 + j*nr; i>=0+j*nr; i--) {
             int_result[i] = int_x[i];
             if(int_result[i] == NA_LOGICAL && gap < maxgap) {
@@ -213,6 +215,7 @@ SEXP na_locf (SEXP x, SEXP fromLast, SEXP _maxgap, SEXP _limit)
             int_result[i] = int_x[i];
           }
           /* result[_first] now has first value fromLast=FALSE */
+          gap = 0;
           for(i=_first+1; i<nr+j*nr; i++) {
             int_result[i] = int_x[i];
             if(int_result[i] == NA_INTEGER) {
@@ -238,6 +241,7 @@ SEXP na_locf (SEXP x, SEXP fromLast, SEXP _maxgap, SEXP _limit)
         /* nr-2 is first position to fill fromLast=TRUE */
         for(j=0; j < nc; j++) {
           int_result[nr-1+j*nr] = int_x[nr-1+j*nr];
+          gap = 0;
           for(i=nr-2 + j*nr; i>=0+j*nr; i--) {
             int_result[i] = int_x[i];
             if(int_result[i] == NA_INTEGER) {
@@ -272,6 +276,7 @@ SEXP na_locf (SEXP x, SEXP fromLast, SEXP _maxgap, SEXP _limit)
             real_result[i] = real_x[i];
           }
           /* result[_first] now has first value fromLast=FALSE */
+          gap = 0;
           for(i=_first+1; i<nr+j*nr; i++) {
             real_result[i] = real_x[i];
             if( ISNA(real_result[i]) || ISNAN(real_result[i])) {
@@ -296,6 +301,7 @@ SEXP na_locf (SEXP x, SEXP fromLast, SEXP _maxgap, SEXP _limit)
       } else {                      /* fromLast=TRUE */
         for(j=0; j < nc; j++) {
           real_result[nr-1+j*nr] = real_x[nr-1+j*nr];
+          gap = 0;
           for(i=nr-2 + j*nr; i>=0+j*nr; i--) {
             real_result[i] = real_x[i];
             if(ISNA(real_result[i]) || ISNAN(real_result[i])) {
@@ -328,6 +334,7 @@ SEXP na_locf (SEXP x, SEXP fromLast, SEXP _maxgap, SEXP _limit)
             SET_STRING_ELT(result, i, STRING_ELT(x, i));
           }
           /* result[_first] now has first value fromLast=FALSE */
+          gap = 0;
           for(i=_first+1; i<nr+j*nr; i++) {
             SET_STRING_ELT(result, i, STRING_ELT(x, i));
             if(STRING_ELT(x, i) == NA_STRING) {
@@ -352,6 +359,7 @@ SEXP na_locf (SEXP x, SEXP fromLast, SEXP _maxgap, SEXP _limit)
       } else {                      /* fromLast=TRUE */
         for(j=0; j < nc; j++) {
           SET_STRING_ELT(result, nr-1+j*nr, STRING_ELT(x, nr-1+j*nr));
+          gap = 0;
           for(i=nr-2 + j*nr; i>=0+j*nr; i--) {
             SET_STRING_ELT(result, i, STRING_ELT(x, i));
             if(STRING_ELT(result, i) == NA_STRING) {