← SASnRConvert Dates to Formatted Character Strings

Introduction

Clinical reports and TFL outputs need dates displayed in specific character formats — "15JAN2025" for listings, "2025-01-15" for ISO compliance, custom layouts for headers.
This is the reverse of parsing: we start with a proper date value and produce a character string in the desired format.
SAS uses the PUT function with a date format; R uses format() with strftime tokens.
A common clinical need is the uppercase month abbreviation ("15JAN2025" not "15jan2025"), which requires an extra step in R.
This lesson converts the same set of dates into several output formats and shows how to get the uppercase month name that clinical displays expect.

Convert Dates to Formatted Character Strings

SAS (Base SAS)+

*=============================================================================;
* Convert date values to formatted character strings
*=============================================================================;

*-----------------------------------------------------------------------------;
* Create sample data with SAS date values
*-----------------------------------------------------------------------------;
data dates;
    input dt :date9.;
    format dt date9.;
    datalines;
15JAN2025
30JUN2025
01DEC2025
;
run;

*-----------------------------------------------------------------------------;
* Convert to various character formats using PUT
*-----------------------------------------------------------------------------;
data formatted;
    set dates;
    length char_date9 $9 char_iso $10 char_e8601 $10 char_custom $11;

    * DATE9. format: 15JAN2025;
    char_date9 = put(dt, date9.);

    * YYMMDD10. format: 2025-01-15;
    char_iso = put(dt, yymmdd10.);

    * E8601DA. format: 2025-01-15 (explicit ISO 8601);
    char_e8601 = put(dt, e8601da.);

    * Custom format with PUTN: DD-MON-YYYY;
    char_custom = put(dt, date9.);
    char_custom = substr(char_custom, 1, 2) || '-' ||
                  substr(char_custom, 3, 5) || '-' ||
                  substr(char_custom, 6, 9);
run;

proc print data=formatted noobs;
run;

We start with three SAS date values and convert each to character strings in several common clinical formats.
put(dt, date9.) produces the standard SAS display format "15JAN2025" — this is the format most commonly used in clinical listings and datasets.
put(dt, yymmdd10.) produces "2025-01-15", which is the ISO 8601 layout expected in SDTM and ADaM character date variables.
put(dt, e8601da.) also produces "2025-01-15" — it is the explicit ISO 8601 date format, functionally identical to yymmdd10. for simple dates.
SAS date formats like DATE9. produce uppercase month abbreviations by default, so no extra step is needed for clinical display standards.
For a custom layout like "DD-MON-YYYY", we apply PUT with DATE9. first and then insert dashes using SUBSTR and concatenation.
The LENGTH statement pre-allocates character variables to the correct width, preventing truncation or excess padding.
We run PROC PRINT and confirm each column contains the expected format — especially the ISO columns, which TFL headers and footnotes often require.

R (tidyverse)+

# =============================================================================
# Convert dates to formatted character strings using lubridate
# =============================================================================
library(tidyverse)
library(lubridate)

# -----------------------------------------------------------------------------
# Create sample data with Date values
# -----------------------------------------------------------------------------
dates <- tibble(
  dt = ymd(c("2025-01-15", "2025-06-30", "2025-12-01"))
)

# -----------------------------------------------------------------------------
# Convert to various character formats
# -----------------------------------------------------------------------------
formatted <- dates %>%
  mutate(
    # DATE9-style: 15JAN2025 (uppercase month abbreviation)
    char_date9 = toupper(format(dt, "%d%b%Y")),

    # ISO format: 2025-01-15
    char_iso = format(dt, "%Y-%m-%d"),

    # Custom DD-MON-YYYY with dashes
    char_custom = toupper(format(dt, "%d-%b-%Y")),

    # Template-based formatting using stamp
    char_stamp = stamp("January 15, 2025", quiet = TRUE)(dt)
  )

print(formatted)

We start with a tibble containing three Date values and convert them to character strings using format() and lubridate helpers.
format(dt, "%d%b%Y") produces "15jan2025" with a lowercase month abbreviation; we wrap it with toupper() to get "15JAN2025" for clinical displays.
format(dt, "%Y-%m-%d") produces the ISO 8601 format "2025-01-15" — no case conversion needed since there are no letters.
format(dt, "%d-%b-%Y") with toupper() gives the custom "15-JAN-2025" layout that some sponsors prefer in listings.
Lubridate's stamp() takes an example string like "January 15, 2025" and builds a formatting function that can be reused across columns.
The quiet = TRUE argument in stamp() suppresses the message about the format it inferred from the example string.
toupper() is the key extra step in R that SAS does not need — R's %b token respects the system locale, which typically produces lowercase month names.
We print the result and confirm the DATE9-style column matches the SAS output exactly.

Happy learning!

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Introduction

Convert Dates to Formatted Character Strings