How to use tapply to match specific condition - r

Question

I have accident dataset that contains number of accidents being reported. I am trying to use tapply function, that will display me the total number of accidents being reported on "Thursday". However, instead of returning number of accidents being reported for particular day. It is displaying total number of rows I have in my dataset.I am using below tapply function.:
tapply(myfinal$VEHICLE_COUNT,myfinal$DAY_OF_WEEK=='THURSDAY',length)
My sample dataset is as follows:
> dput(tail(myfinal,5))
structure(list(CASE_NUMBER = c("1251045636", "1251045630", "1251045591",
"1251045574", "1250010434"), BARRACK = c("Frederick", "Frederick",
"Frederick", "Frederick", "Jessup"), ACC_DATE = c("2012-12-31T00:00:00",
"2012-12-31T00:00:00", "2012-12-31T00:00:00", "2012-12-31T00:00:00",
"2012-12-31T00:00:00"), ACC_TIME = c("18:12", "18:12", "12:12",
"9:12", "11:12"), ACC_TIME_CODE = c("5", "5", "4", "3", "3"),
DAY_OF_WEEK = c("MONDAY ", "MONDAY ", "MONDAY ", "MONDAY ",
"MONDAY "), ROAD = c("IS 00070 EISENHOWER MEMOR HWY", "MD 00077 ROCKY RIDGE RD",
"MD 00085 BUCKEYSTOWN PIKE", "MD 00017 MYERSVILLE RD", "IS 00070 No Name"
), INTERSECT_ROAD = c("CO 00248 MONUMENT RD", "MD 00076 MOTTERS STATION RD",
"CO 00308 MANOR WOODS RD", "CO 00941 DAWN CT", "US 00029 Columbia Pike"
), DIST_FROM_INTERSECT = c("300", "0", "400", "500", "0.25"
), DIST_DIRECTION = c("E", "U", "S", "S", "E"), CITY_NAME = c("Not Applicable",
"Not Applicable", "Not Applicable", "Not Applicable", NA),
COUNTY_CODE = c("10", "10", "10", "10", "13"), COUNTY_NAME = c("Frederick",
"Frederick", "Frederick", "Frederick", "Howard"), VEHICLE_COUNT = c(1,
2, 2, 1, 2), PROP_DEST = c("NO", "YES", "YES", "NO", "NO"
), INJURY = c("YES", "NO", "NO", "YES", "YES"), COLLISION_WITH_1 = c("FIXED OBJ",
"VEH", "VEH", "NON-COLLISION", "VEH"), COLLISION_WITH_2 = c("OTHER-COLLISION",
"OTHER-COLLISION", "OTHER-COLLISION", "OTHER-COLLISION",
"OTHER-COLLISION")), .Names = c("CASE_NUMBER", "BARRACK",
"ACC_DATE", "ACC_TIME", "ACC_TIME_CODE", "DAY_OF_WEEK", "ROAD",
"INTERSECT_ROAD", "DIST_FROM_INTERSECT", "DIST_DIRECTION", "CITY_NAME",
"COUNTY_CODE", "COUNTY_NAME", "VEHICLE_COUNT", "PROP_DEST", "INJURY",
"COLLISION_WITH_1", "COLLISION_WITH_2"), row.names = 18634:18638, class = "data.frame")
Any suggestions on how to fix it! Thanks in advance!

Answer 1

If can only use tapply for whatever reason, then, building off of Maurits' answer, you should be able to do this:
tapply(myfinal$VEHICLE_COUNT,trimws(myfinal$DAY_OF_WEEK)=='THURSDAY',length)
Or similar. It seems that the strings in your DAY_OF_WEEK variable have a lot of whitespaces at the end. You either need to remove them (via trimws) or modify your comparison string to include these spaces (e.g., myfinal$DAY_OF_WEEK=="THURSDAY "). With the comparison operator, R will match two string only if they match exactly character by character, so any additional whitespaces in either string will count against you.

Answer 2

Base R solution is to subset DAY_OF_WEEK by "THURSDAY" and then return number of rows:
nrow(df[df$DAY_OF_WEEK == "THURSDAY",])

Answer 3

There is really no point in using tapply here!
Method 1
Use dplyr:
require(tidyverse);
df %>% filter(trimws(DAY_OF_WEEK) == "MONDAY") %>% summarise(count = n());
# count
#1 5
Method 2
In base R, use subset and table
table(subset(df, trimws(DAY_OF_WEEK) == "MONDAY")$DAY_OF_WEEK);
#MONDAY
# 5
I've used "MONDAY" here because you've got no entries with DAY_OF_WEEK = "THURSDAY".
Sample data
df <- structure(list(CASE_NUMBER = c("1251045636", "1251045630", "1251045591",
"1251045574", "1250010434"), BARRACK = c("Frederick", "Frederick",
"Frederick", "Frederick", "Jessup"), ACC_DATE = c("2012-12-31T00:00:00",
"2012-12-31T00:00:00", "2012-12-31T00:00:00", "2012-12-31T00:00:00",
"2012-12-31T00:00:00"), ACC_TIME = c("18:12", "18:12", "12:12",
"9:12", "11:12"), ACC_TIME_CODE = c("5", "5", "4", "3", "3"),
DAY_OF_WEEK = c("MONDAY ", "MONDAY ", "MONDAY ", "MONDAY ",
"MONDAY "), ROAD = c("IS 00070 EISENHOWER MEMOR HWY", "MD 00077 ROCKY RIDGE RD",
"MD 00085 BUCKEYSTOWN PIKE", "MD 00017 MYERSVILLE RD", "IS 00070 No Name"
), INTERSECT_ROAD = c("CO 00248 MONUMENT RD", "MD 00076 MOTTERS STATION RD",
"CO 00308 MANOR WOODS RD", "CO 00941 DAWN CT", "US 00029 Columbia Pike"
), DIST_FROM_INTERSECT = c("300", "0", "400", "500", "0.25"
), DIST_DIRECTION = c("E", "U", "S", "S", "E"), CITY_NAME = c("Not Applicable",
"Not Applicable", "Not Applicable", "Not Applicable", NA),
COUNTY_CODE = c("10", "10", "10", "10", "13"), COUNTY_NAME = c("Frederick",
"Frederick", "Frederick", "Frederick", "Howard"), VEHICLE_COUNT = c(1,
2, 2, 1, 2), PROP_DEST = c("NO", "YES", "YES", "NO", "NO"
), INJURY = c("YES", "NO", "NO", "YES", "YES"), COLLISION_WITH_1 = c("FIXED OBJ",
"VEH", "VEH", "NON-COLLISION", "VEH"), COLLISION_WITH_2 = c("OTHER-COLLISION",
"OTHER-COLLISION", "OTHER-COLLISION", "OTHER-COLLISION",
"OTHER-COLLISION")), .Names = c("CASE_NUMBER", "BARRACK",
"ACC_DATE", "ACC_TIME", "ACC_TIME_CODE", "DAY_OF_WEEK", "ROAD",
"INTERSECT_ROAD", "DIST_FROM_INTERSECT", "DIST_DIRECTION", "CITY_NAME",
"COUNTY_CODE", "COUNTY_NAME", "VEHICLE_COUNT", "PROP_DEST", "INJURY",
"COLLISION_WITH_1", "COLLISION_WITH_2"), row.names = 18634:18638, class = "data.frame")