counting occurence of character - bash

Question

I have a file that looks like this
chr1A_p1
chr1A_p2
chr10B_p1
chr10A_p1
chr11D_p2
chr18B_p2
chr9D_p1
I need to count number of time A, B & D occur. Individually, I would do it like this
awk '{if($1~/A/) print $0 }' < test.txt | wc
awk '{if($1~/B/) print $0 }' < test.txt | wc
awk '{if($1~/D/) print $0 }' < test.txt | wc
How to join these lines so that I can count number of A,B,D just through one liner instead of 3 separate lines.

Answer 1

For specific line format (where the needed char is before _):
$ awk -F"_" '{ seen[substr($1, length($1))]++ }END{ for(k in seen) print k, seen[k] }' file
A 3
B 2
D 2

Answer 2

Counting occurrences is generally done by keeping track of a counter. So a single of the OP's awk lines;
awk '{if($1~/A/) print $0}' < test.txt | wc
can be rewritten as
awk '($1~/A/){c++}END{print c}' test.txt
for multiple cases, you can now do:
awk '($1~/A/){c["A"]++}
($1~/B/){c["B"]++}
($1~/D/){c["D"]++}
END{for(i in c) print i,c[i]}' test.txt
Now you can even clean this up a bit more:
awk '{c["A"]+=($1~/A/)}
{c["B"]+=($1~/B/)}
{c["D"]+=($1~/D/)}
END{for(i in c) print i,c[i]}' test.txt
which you can clean up further as:
awk 'BEGIN{split("A B D",a)}
{for(i in a) c[a[i]]+=($1~a[i])}
END{for(i in c) print i,c[i]}' test.txt
But these cases just count how many times a line occurs that contains the letter, not how many times the letter occurs.
awk 'BEGIN{split("A B D",a)}
{for(i in a) c[a[i]]+=gsub(a[i],"",$1)}
END{for(i in c) print i,c[i]}' test.txt

Answer 3

Perl to the rescue!
perl -lne '$seen{$1}++ if /([ABD])/; END { print "$_:$seen{$_}" for keys %seen }' < test.txt
-n reads the input line by line
-l removes newlines from input and adds them to output
a hash table %seen is used to keep the number of occurrences of each symbol. Each time it's matched it's captured and the corresponding field in the hash is incremented.
END is run when the file ends. It outputs all the keys of the hash, i.e. the matched characters, each followed by the number of occurrences.

Answer 4

datafile:
chr1A_p1
chr1A_p2
chr10B_p1
chr10A_p1
chr11D_p2
chr18B_p2
chr9D_p1
script.awk
BEGIN {
arr["A"]=0
arr["B"]=0
arr["D"]=0
}
/A/ { arr["A"]++ }
/B/ { arr["B"]++ }
/D/ { arr["D"]++ }
END {
printf "A: %s, B: %s, D: %s", arr["A"], arr["B"], arr["D"]
}
execution:
awk -f script.awk datafile
result:
A: 3, B: 2, D: 2