Login or Register to Ask a Question and Join Our Community


Shell Programming and Scripting

Find Where Values Change From Positive To Negative and viceversa

Login to Discuss or Reply to this Discussion in Our Community

 
Thread Tools Search this Thread
Top Forums Shell Programming and Scripting Find Where Values Change From Positive To Negative and viceversa
# 1  
Old 03-11-2011
Find Where Values Change From Positive To Negative and viceversa
Hi all,

I have a file that looks like shown below. I want to find places where the value in column 2 change from negative to positive and vice versa and return the value on column 1 at that point. I wonder if this is possible in shell script or awk .. please help!

Here is the original data

Quote:
2.91 -1.19 1.34 78.00 2.00
3.09 -1.21 1.33 91.00 2.00
3.28 -1.03 1.41 87.00 2.00
3.47 -0.78 1.48 86.00 2.00
3.66 -0.47 1.51 86.00 2.00
3.84 0.01 1.42 88.00 2.00
4.03 0.47 1.15 85.00 2.00
4.22 0.93 0.45 87.00 2.00
4.41 1.00 0.00 87.00 1.00
4.59 1.00 0.00 87.00 1.00
4.78 1.00 0.00 87.00 1.00
4.97 1.00 0.00 84.00 1.00
5.16 1.00 0.00 88.00 1.00
5.34 1.00 0.00 86.00 1.00
8.53 1.00 0.00 86.00 1.00
8.72 1.00 0.00 87.00 1.00
8.91 1.00 0.00 78.00 1.00
9.09 1.00 0.00 91.00 1.00
9.28 1.00 0.00 87.00 1.00
9.47 1.00 0.00 86.00 1.00
9.66 1.00 0.00 86.00 1.00
9.84 1.00 0.00 88.00 1.00
10.03 0.54 1.09 85.00 2.00
10.22 -0.86 1.46 87.00 2.00
10.41 -1.86 0.63 87.00 2.00
10.59 -1.76 0.82 87.00 2.00
10.78 -0.83 1.47 87.00 2.00
10.97 0.07 1.40 84.00 2.00
11.16 0.80 0.76 88.00 2.00
11.34 1.00 0.00 86.00 1.00
And the desired output is

Quote:
3.66
10.03
10.78
Is there a way I can do this? And sorry I am a real newbie in shell scripting and I have no clue how to start this and so I have no suggested code

Thank you very much for your assistance and advice
Malandisa
# 2  
Old 03-11-2011
Code:
nawk 'FNR==1{prev1=$1;prev2=$2;next}($2*prev2<0){print prev1}{prev1=$1;prev2=$2}' myFile

# 3  
Old 03-11-2011
Oh! wow!

Works exactly what I needed! I surely need to have a manual/book for awk/nawk

Thanks you so much ..vgersh99
# 4  
Old 03-21-2011
Hi vgersh99 and all,

Thank you for your help. The solution you gave works well, just a small problem I am not able to solve and have tried to do this by mysellf as a way to learn more how to use awk. but over a week now I can solve this. The problem is the solution above fails if the number just before or just before the negative numbers is 0.00. see the data

Here the data and see what happens

Quote:
2.91 -1.19 1.34 78.00 2.00
3.09 -1.21 1.33 91.00 2.00
3.28 -1.03 1.41 87.00 2.00
3.47 -0.78 1.48 86.00 2.00
3.66 -0.47 1.51 86.00 2.00
3.84 0.00 1.42 88.00 2.00
4.03 0.47 1.15 85.00 2.00
4.22 0.93 0.45 87.00 2.00
4.41 1.00 0.00 87.00 1.00
4.59 1.00 0.00 87.00 1.00
4.78 1.00 0.00 87.00 1.00
4.97 1.00 0.00 84.00 1.00
5.16 1.00 0.00 88.00 1.00
5.34 1.00 0.00 86.00 1.00
8.53 1.00 0.00 86.00 1.00
8.72 1.00 0.00 87.00 1.00
8.91 1.00 0.00 78.00 1.00
9.09 1.00 0.00 91.00 1.00
9.28 1.00 0.00 87.00 1.00
9.47 1.00 0.00 86.00 1.00
9.66 1.00 0.00 86.00 1.00
9.84 1.00 0.00 88.00 1.00
10.03 0.00 1.09 85.00 2.00
10.22 -0.86 1.46 87.00 2.00
10.41 -1.86 0.63 87.00 2.00
10.59 -1.76 0.82 87.00 2.00
10.78 -0.83 1.47 87.00 2.00
10.97 0.07 1.40 84.00 2.00
11.16 0.80 0.76 88.00 2.00
11.34 1.00 0.00 86.00 1.00
See how this fails to give the correct result as when the data is as given in my initial post.

I have been thinking a solution would be to use some if statement but I have not managed to find a way to use an iff statement in this case.

I sincerely appreciate you assistance.

Thank you
Malandisa
# 5  
Old 03-21-2011
how about this:
Code:
$ nawk 'FNR>1&&$2*prev2<0{print prev1}$2{prev1=$1;prev2=$2}' myFile
3.66
9.84
10.78

or this:
Code:
$ awk 'FNR>1&&$2*prev2<0{print prev1}{prev1=$1;if($2)prev2=$2}' myFile
3.84
10.03
10.78

Last edited by Chubler_XL; 03-21-2011 at 11:36 PM..
# 6  
Old 03-21-2011
Thank you Chubler_XL! it works perfectly. I thought I had understood this command but I realize I have not fully understood what the command really does. My understanding was that this part
Quote:
($2*prev2<0)
represents an if statement so that if it is satisfied, then the part in curly brackets '{}' just to the right is performed. And now I am not sure how the addition of the '$2' solves this problem

Thank you again
# 7  
Old 03-22-2011
You are correct awk programs consist of any number of <COND> { <statements> } if <COND> is left out or has a value of true for a particular line the statements are executed.

The program I supplied has two of these:

Code:
FNR>1&&$2*prev2<0{print prev1}

if rownumber of input file > 1 and 2nd field multiplied by prev2 < 0 (ie 2nd field and prev2 have different sign) it will print prev1
B.T.W the test on rownumber is unnecessary as prev2 will have null on 1st line and null*value will always be zero (and so not < zero). So removing FNR>1&& would produce the same results.

Code:
$2{prev1=$1;prev2=$2}

if 2nd field is non-zero then prev1=1st fld ; prev2=2nd fld
Last edited by Chubler_XL; 03-22-2011 at 12:59 AM..
Login or Register to Ask a Question

Previous Thread | Next Thread

9 More Discussions You Might Find Interesting

1. UNIX for Beginners Questions & Answers

Splitting a file based on negative and positive numbers

I have a file that is pipe delimited and in Column F they have number values, both positive and negative. I need to take the one file I am starting with and split it into two separate files based on negative and positive numbers. What is the command to do so? And then I need to also transfer... (4 Replies)
Discussion started by: cckaiser15
4 Replies

2. UNIX for Beginners Questions & Answers

Converting negative number to positive in a file

Hi ALL, I am having semi column separated file as below. I am having negative values for the records starting with 11095. How can I convert that positive number I tried this below seems not working sed 's/ \(*\)$/ -\1/;t;s/\(.*\)-/\1/ myfile myfile... (6 Replies)
Discussion started by: arunkumar_mca
6 Replies

3. Shell Programming and Scripting

Splitting a file based on positive and negative numbers

Dear All, I have to split a tab delimited file in two files based on the presence of a positive or negative in column number 9 , for example file: A 1 5 erg + 6766 0.9889 0.9817 9.01882 erg inside upstream B 1 8 erg2 + 6766 0.9889 0.9817 -9.22 erg2 inside... (3 Replies)
Discussion started by: paolo.kunder
3 Replies

4. Shell Programming and Scripting

Taking largest (negative) number from column of coordinates and adding positive form to every other

Hello all, I'm new to the forums and hope to be able to contribute something useful in the future; however I must admit that what has prompted me to join is the fact that currently I need help with something that has me at the end of my tether. I have a PDB (Protein Data Bank) file which I... (13 Replies)
Discussion started by: crunchgargoyle
13 Replies

5. Shell Programming and Scripting

addition of both positive and negative numbers

Let, I have three numbers +00123.25 -00256.54 +00489.23 I need to sum up all those three numbers, after storing them in three variables (say var1, var2, var3). I used both expr and BC, but they didn't work for me. But, I am not able to sum up them, as I don't have any idea how to... (13 Replies)
Discussion started by: mady135
13 Replies

6. Shell Programming and Scripting

Sorting positive and negative values

Hello, I have a list like this : 1 2 -4 0 -3 -7 5 6 etc. Is there a way to remove all the positive values and print only the negative values, without using grep, sed or awk? Thanks, Prasanna (4 Replies)
Discussion started by: prasanna1157
4 Replies

7. Shell Programming and Scripting

Finding the most positive and negative value and defining its position

Hi, I have a file that looks like this: Jake 2 3 4 6 4 3 -2 -1 Jerry 1 2 3 2 1 7 -6 -1 Timmy -1 -4 -5 -8 9 3 1 I want to find the most positive and negative value for each row and also define its position (based on column #) So the output would look... (7 Replies)
Discussion started by: gisele_l
7 Replies

8. Shell Programming and Scripting

Perl output with negative and positive numbers

Hello, For my weather station I have made a little perl script to put the data into cacti. The next problem I have. I can only get positive numbers or negative numbers. What do I do: Though a shell scrip I call the perl script. Shell script: #!/bin/sh cat data.txt | stats.pl Perl... (4 Replies)
Discussion started by: rbl-blacklight
4 Replies

9. Shell Programming and Scripting

Help in adding positive & negative values in a column

Hi Gurus, In my file I have an amount field from position 74 to 87, which contains values starting with '+' as well as '-'. I want to add all positive values in a varible called "CREDIT" and all negative values in a variable "DEBIT". I know, we can use grep to identify values with positive and... (4 Replies)
Discussion started by: berlin_germany
4 Replies
Login or Register to Ask a Question