AWK filter first and last row of given variable, discard the middle rows

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I am trying to filter a file by selecting the first and last row of a given variable in a tab-delimited txt file using AWK.

Tab-delimited file looks like this:

1 apple  30
2 apple  35
3 apple  36
4 apple  20
5 pear   10
6 pear   30
7 pear   45
8 orange 16 

END 

and I am trying to process this using awk, to only print the first and last rows of each variable in $2 (the fruit column in this example)

The file I actually have is ~ 35000 rows in length, and has 3000 unique variables in the column i'm wanting to use as the filter (so in this above example col2)

I was thinking the approach would be to create an array of unique col2 values, (apple, pear, orange) and then using this array extract the first and last values from the larger file... but some advise on the nomenclature needed to select the first and last row per indexed variable would be greatly appreciated. :)

INPUT file given above, expected output would be

1 apple  30
4 apple  20
5 pear   10
7 pear   45
8 orange 16

the output needs to include those with only one entry too (the orange in this case)

One way:

awk '$2!=prev{if (pline){print pline;}print;}{prev=$2;pline=$0;}END{print pline;}' file | uniq

Print every time a new 2nd column line is encountered. While printing the new 2nd column line, if the prev line is not empty, print that as well. uniq is to remove the the duplicate lines which gets printed in case of single record present in between.

Rows and Columns – A Primer for Computational Biology, The awk command that we want, printing only those lines where the first two columns statements in the unadorned middle block are executed for every line, and The special variable NF holds the number of columns (also known as fields) in on the BLAST output above, after filtering out comment lines with grep -v '#' . I am trying to filter a file by selecting the first and last row of a given variable in a tab-delimited txt file using AWK. Tab-delimited file looks like this: 1 apple 30 2 apple 35 3 apple 36 4 apple 20 5 pear 10 6 pear 30 7 pear 45 8 orange 16 END

This will work even if the same data appears as both the first and last line for a given key value or if the data contained blank or 0 lines (assuming you'd want those handled just like every other line, easily skipped if not):

$ cat tst.awk
$2 != prev2 {
    if ( NR > 1 ) {
        print rec
    }
    beg = rec = $0
    prev2 = $2
    next
}
{ rec = beg ORS $0 }
END { print rec }

$ awk -f tst.awk file
1 apple  30
4 apple  20
5 pear   10
7 pear   45
8 orange 16

Using AWK to Filter Rows � Tim Dennis, She sent me the below sample file and how she wanted to filter it. NF is an AWK built in variable and it stands for number of fields. will print the number of columns for each row and since each row has Now we've selected a couple of columns to print out, let's use AWK to search for a specific thing – a� awk to print the first column. The first column of any file can be printed by using $1 variable in awk. But if the value of the first column contains multiple words then only the first word of the first column prints. By using a specific delimiter, the first column can be printed properly. Create a text file named students.txt with the

tried on gnu awk, no need external program

awk '{if($0~/^[a-z0-9]/) a[NR]=$0} END{f=1;asort(a); for(;i++<NR;){split(a[i],b);if(b[2]==$2||f){$1=b[1];$2=b[2];$3=b[3];if(f){f=0;print}} else if(b[2]){print;print b[1],($2=b[2]),b[3]}} }' d

How do I delete the first n lines and last line of a file using shell , In which case the following command will strip first and last lines from input: ( quoted so that the shell doesn't think it's a variable) deletes the last line, w writes the file and q You can use awk as it handles both pattern matching and line counting, You can use head and tail to trim specific counts of lines, The first line found was a comment line, and although the “UUID” string is in the middle of it, awk still found it. We can tweak the regular expression and tell awk to process only lines that start with “UUID.” To do so, we type the following which includes the start of line token (^): awk '/^UUID/ {print $0}' /etc/fstab

awk to print first row with forth column and last row with fifth column , And another question is that if there is to print first row with fourth column and last row with fifth column; in each file; how the solution with awk will be? script that uses awk to read two lines from a file and write just column 4 from the 1st row Is it possible to remove redundant names in the 4th column? input cqWE 100 200�

10 Awk Tips, Tricks and Pitfalls, Suppose one wants to print all the lines in a file that match some pattern (a kind of The first thing to note is that it is not structured according to the awk's lines (or: removes empty lines, where NF==0) awk 'NF--' # removes last field and prints The special variable NR stores the total number of input records read so far,�

How to Use Awk and Regular Expressions to Filter Text or String in , Skip to content In order to filter text, one has to use a text filtering tool such as awk. It works by reading a given line in the file, makes a copy of the line and then It will match strings containing localhost, localnet, lines, capable, And (*) in /t*t/ wild card character allows awk to choose the the last option:

Comments
  • Is the file sorted on column2?
  • Hi, yes the file is sorted on column 2.