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isoweek()/isoyear(): compute in C via convertDate() #7951

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Merged
ben-schwen merged 1 commit into from
Nov 1, 2026
+22 −11
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isoweek()/isoyear(): compute in C via convertDate() #7951

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13 changes: 3 additions & 10 deletions R/IDateTime.R
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Original file line number Diff line number Diff line change
Expand Up @@ -393,15 +393,8 @@ yday = function(x) convertDate(as.IDate(x), "yday")
wday = function(x) convertDate(as.IDate(x), "wday")
mday = function(x) convertDate(as.IDate(x), "mday")
week = function(x) convertDate(as.IDate(x), "week")
# ISO 8601-conformant week, as described at
# https://en.wikipedia.org/wiki/ISO_week_date
# Approach:
# * Find nearest Thursday to each element of x
# * Find the number of weeks having passed between
# January 1st of the year of the nearest Thursdays and x
nearest_thurs = function(x) 7L * ((as.integer(as.IDate(x)) + 3L) %/% 7L)
isoweek = function(x) (convertDate(nearest_thurs(x), "yday") - 1L) %/% 7L + 1L
isoyear = function(x) convertDate(nearest_thurs(x), "year")
isoweek = function(x) convertDate(as.IDate(x), "isoweek")
isoyear = function(x) convertDate(as.IDate(x), "isoyear")

month = function(x) convertDate(as.IDate(x), "month")
quarter = function(x) convertDate(as.IDate(x), "quarter")
Expand Down Expand Up @@ -432,6 +425,6 @@ yearqtr = function(x, format = c("numeric", "character")) {
}

convertDate = function(x, type) {
type = match.arg(type, c("yday", "wday", "mday", "week", "month", "quarter", "year", "yearmon", "yearqtr"))
type = match.arg(type, c("yday", "wday", "mday", "week", "isoweek", "isoyear", "month", "quarter", "year", "yearmon", "yearqtr"))
.Call(CconvertDate, x, type)
}
20 changes: 19 additions & 1 deletion src/idatetime.c
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@ static const int YEARS100 = 36524;
static const int YEARS4 = 1461;
static const int YEARS1 = 365;

typedef enum { YDAY, WDAY, MDAY, WEEK, MONTH, QUARTER, YEAR, YEARMON, YEARQTR} datetype;
typedef enum { YDAY, WDAY, MDAY, WEEK, ISOWEEK, ISOYEAR, MONTH, QUARTER, YEAR, YEARMON, YEARQTR} datetype;

static inline bool isLeapYear(int year) {
return (year % 100 != 0 || year % 400 == 0) && year % 4 == 0;
Expand All @@ -29,6 +29,22 @@ void convertSingleDate(int x, datetype type, void *out)
return;
}

if (type == ISOWEEK || type == ISOYEAR) {
// ISO 8601-conformant week, as described at https://en.wikipedia.org/wiki/ISO_week_date
// The ISO week and year are those of the nearest Thursday
// Thursdays are multiples of 7, since x=0 (1970-01-01) was a Thursday
int thu = x + (3 - (x % 7 + 10) % 7);
int res;
if (type == ISOWEEK) {
convertSingleDate(thu, YDAY, &res);
res = (res - 1) / 7 + 1;
} else {
convertSingleDate(thu, YEAR, &res);
}
*(int *)out = res;
return;
}

int days = x - 11017;

int years400 = days / YEARS400;
Expand Down Expand Up @@ -134,6 +150,8 @@ SEXP convertDate(SEXP x, SEXP type)
else if (!strcmp(ctype_str, "wday")) ctype = WDAY;
else if (!strcmp(ctype_str, "mday")) ctype = MDAY;
else if (!strcmp(ctype_str, "week")) ctype = WEEK;
else if (!strcmp(ctype_str, "isoweek")) ctype = ISOWEEK;
else if (!strcmp(ctype_str, "isoyear")) ctype = ISOYEAR;
else if (!strcmp(ctype_str, "month")) ctype = MONTH;
else if (!strcmp(ctype_str, "quarter")) ctype = QUARTER;
else if (!strcmp(ctype_str, "year")) ctype = YEAR;
Expand Down
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