You may need to merge several pdf-files into one.

There are several tools. Some of them you have to pay for.

If you are in a linux environment, try this:

gs -dBATCH -dNOPAUSE -q -sDEVICE=pdfwrite -sOutputFile=final.pdf filea.pdf fileb.pdf

continue with filec.pdf etc.

Some say it is slow.

Others say, yes it is slow, but it produces smaller final files, and are able to handle “difficult pdfs”.

I say it is nice that it can be done from the command line.

Linux have a lot of small tools, that only does one thing. But do it really well (compare to Windows, that has a lot of large tools that does everything rather badly).

This is really just a note to myself. These tools are really useful but they are not (yet) second nature to me. I often find myself in the situation, where I know there is a tool for something, that I have used several times before. But simply can’t remember what it was.

grep. Searches files for lines matching a regular expression. Useful parameters (or at least parameters I have a regular use for):

-c returns a count of the lines matching.
-n returns the linenumber (in the file) of the matching line.

tail. returns the last part of a file

-n 6 returns the last 6 lines of the file (standard 10)

head. Returns the first part of a file

-n 6 returns the first 6 lines of the file (standard 10)

cut. Removes sections of lines in a file (or other input)

-d x. Splits the line at x. Use ‘ ‘ for space
-f 1. Select the first field.

wc. Counts stuff in files.

-l. counts the lines in the file (or other input)
-w count the words in the file (or other input)

|. Piping. Takes the result of the command in front of it, and pass it to the command after it (and that is the direction. If you find examples on Stackoverflow that will only give the desired result if the direction is reversed, don’t be surprised if it does not work…)

cat. Prints one or more files to standard output (your screen).

But if we print to another output, eg with “> file.name”, we can concatenate several files.

find. Searches for files. “find .” finds everything. Pipe it to grep to search for something specific. eg “find . | grep ‘acta'” to find all files containing the string “acta”.

-print prints the complete filename.
-print0 prints the complete filename even if it includes a newline.

csvsql. Commandline tool for analysing csv-files using sql-syntax

csvstat. Commandline tool for analysing csv-files

Because you often find the solution to your excel problem on an english language site. But have to solve the problem in a danish version of Excel.
Remember that you also have to change “,” to “;”

Given a set of data, where some values indicate that they are the same as a previous value, how to replace them with the correct value.

Eg, this dataframe:

(m <- data.frame(i=c(1:10,NA), t=c("lorem", "do", "do", "Do", "ipsum", "do", "Do", "(do)", "dolor", NA, "test"), stringsAsFactors=F))

##     i     t
## 1   1 lorem
## 2   2    do
## 3   3    do
## 4   4    Do
## 5   5 ipsum
## 6   6    do
## 7   7    Do
## 8   8  (do)
## 9   9 dolor
## 10 10  <NA>
## 11 NA  test

How to replace the first three “do”s with “lorem” and the next set of “do”s with “ipsum”

Using fill() from the tidyr package is straight forward. It takes a vector, locates all NA, and replaces them with the last, non-NA value.
Simple enough, change all the variations of “do” to NA, run fill(). Done.
One problem, there might be NAs in the dataset, that we do not want to affect.
Solution – there might be a more elegant one, but this works:

1. Change the NAs to something that do not occur in the data
2. Change to variations of “do” to NA
3. Use the fill()-function
4. Change the NAs from step 1 back to NA

library(tidyr)
rpl <- "replacement"
m[is.na(m$t),]$t <- rpl
doset <- c("do", "Do", "(do)")
m[(m$t %in% doset),]$t <- NA

m <- m %>% fill(t)
m[(m$t == rpl),]$t <- NA
m

##     i     t
## 1   1 lorem
## 2   2 lorem
## 3   3 lorem
## 4   4 lorem
## 5   5 ipsum
## 6   6 ipsum
## 7   7 ipsum
## 8   8 ipsum
## 9   9 dolor
## 10 10  <NA>
## 11 NA  test

Done!

Oh, and by the way, this is my first post generated directly from RStudio.