Find the next nearest value (bash) - linux

Question

Let's say I have some holiday data (holiday_master.csv) in columns, something like
...
20200320 Vernal Equinox Day
20200429 Showa Day
20200503 Constitution Day
20200505 Green Day
20200720 Children's Day
20200811 Sea Day
...
Given this set of data, I want to find the next closest holiday from the given date.
For example if the input is 20200420, 20200429 Showa Day is expected.
If the input is 20200620, 20200720 Children's Day is expected.
I have a feeling that awk has the necessary functionality to do this, but any solution that works in a bash script is welcome.

Answer 1

Would you please try the bash script:
#!/bin/bash
input="20200428" # or assign to whatever
< "holiday_master.csv" sort -nk1,1 | # sort the csv file by date and pass to the while loop
while read -r date desc; do
if (( date >= input )); then # if the date is greater than or equal to the input
echo "$date" "$desc" # then print the line
break # and exit the loop
fi
done

Answer 2

Assuming no two days will ever have the same date...
DATE=<some desired input date>
awk "{print (\$1 - $DATE"' "\t" $0)}' calendar.txt | sed '/^-/d' | sort | head -n 1 | awk '{$1=""; print $0}'
Explanation
awk "{print (\$1 - $DATE"' "\t" $0)}' calendar.txt: Prepend a column to the input.txt file describing the difference between the desired input date and the date column
sed '/^-/d': Remove all lines beginning with -. Dates with negative differences have already passed.
sort: Sort the remaining entries from least to greatest (based upon the difference column)
head -n 1: Select only the first row (The lowest difference)
awk '{$1=""; print $0}': Print all but the first column
Prettier script version
#!/bin/bash
# Usage: script <Date> <Calendar file>
DATE=${1:--1}
CAL=${2:-calendar.txt}
# Arg check and execute
if[ ! -f $CAL ]
then
echo "File not found: $CAL"
echo "Usage: script <Date> <Calendar file>"
elif [ $DATE -le 0 ]
then
echo "Invalid date: $DATE"
echo "Usage: script <Date> <Calendar file>"
elif [ $(echo "$DATE" | grep -Ewo -- '-?[0-9]+' | wc -l) -eq 0 ]
then
echo "Invalid date: $DATE"
echo "Usage: script <Date> <Calendar file>"
else
awk '{print ($1 - '"$DATE"' "\t" $0)}' $CAL | sed '/^-/d' | sort | head -n 1 | awk '{$1=""; print $0}'
fi

Answer 3

As you use YYYYMMDD format we might compare it just like numbers (note: year is greater than month, month is greater than day). So you can use AWK following way, let:
20200320 Vernal Equinox Day
20200429 Showa Day
20200503 Constitution Day
20200505 Green Day
20200720 Children's Day
20200811 Sea Day
be file named holidays.txt then:
awk 'BEGIN{inputdate=20200420}{if($1>inputdate){print $2;exit}}' holidays.txt
output:
Showa
Explanation: in BEGIN I set inputdate to 20200420 then when line with greater number in 1st column is found I print content of 2nd column and exit (otherwise later dates would be printed too). Note that AWK does automatically parse number when asked to do comparison (> in this case) so you do not have to care about conversion yourself - you could even do inputdate="20200420" and it would work too.
This solution assumes that all dates in file are already sorted.

Answer 4

Using awk and assuming the source data is comma separated:
awk -F, -v dayte="20200420" '
BEGIN {
"date -d "dayte" +%s" | getline dat1
{
{
"date -d "$1" +%s" | getline dat2;
dat3=dat2-dat1;
if (dat3 > 0 )
{
hols[dat3]=$2
}
}
END {
asorti(hols,hols1,"#ind_num_asc");
print hols[hols1[1]]
}
' holiday_master.csv
One liner:
awk -F, -v dayte="20200420" 'BEGIN { "date -d "dayte" +%s" | getline dat1 } { "date -d "$1" +%s" | getline dat2;dat3=dat2-dat1;if (dat3 > 0 ) { hols[dat3]=$2 } } END { asorti(hols,hols1,"#ind_num_asc");print hols[hols1[1]] }' holiday_master.csv
Set the field separator to , and set a variable dayte to the date we wish to check. In the BEGIN block, we pass the dayte variable through to date command via an awk pipe/getline and read the epoch result into the variable dat1. We do the same with the first column on the master file ($1) and read this into dat2. We take the difference between the epoch dates and read the result into dat3. Only if the result is positive (in the future) do we then use dat3 for an index in a "hols" array, with the holiday description as the value. In the END block, we sort the indexes of hols into a news hols1 array basing the sort on ascending, numeric indexes. We then take the first index of the new hols1 array to attain the holiday that is closest to the dayte variable.

Answer 5

Assuming the holiday list file is sorted by date as you have given, the below would work
$ awk -v dt="20200420" ' (dt-$1)<0 { print;exit } ' holiday.txt
20200429 Showa Day
$ awk -v dt="20200620" ' (dt-$1)<0 { print;exit } ' holiday.txt
20200720 Children's Day
$
If the holiday file is not sorted, then you can use below
$ shuf holiday.txt | awk -v dt="20200420" ' dt-$1<0 { a[(dt-$1)*-1]=$0 } END { asort(a); print a[1] } '
20200429 Showa Day
$ shuf holiday.txt | awk -v dt="20200620" ' dt-$1<0 { a[(dt-$1)*-1]=$0 } END { asort(a); print a[1] } '
20200720 Children's Day