zero padding regex dependent on length of digits

Question

I have a field which contains two charecters, some digits and potentially a single letter. For example

QU1Y
ZL002
FX16
TD8
BF007P
VV1395
HM18743
JK0001

I would like to consistently return all letters in their original position, but digits as follows.

for 1 to 3 digits : return all digits OR the digits left padded with zeros

For 4 or more digits : it must not begin with a zero and return the 4 first digits OR if the first is a zero then truncate to three digits

example from the data above

QU001Y
ZL002
FX016
TD008
BF007P
VV1395
HM1874
JK001

The implementation will be in R but I'm interested in a straight regex solution, I'll work out the R side of things. It may not be possible in straight regex which is why I can't get my head round it.

This identifies the correct ones, but I'm hoping to correct those which are not right.

"[A-Z]{2}[1-9]{0,1}[0-9]{1,3}[F,Y,P]{0,1}"

For the curious, they are flight numbers but entered by a human. Hence the variety...

You won't be able to solve it without a bit of code. Use `gsubfn` once you are sure you know the right pattern to match the strings where modification is required. — Wiktor Stribiżew, Oct 08 '18 at 12:47
If the first two letters must exist, use `gsubfn('^[A-Z]{2}\\K0*(\\d{1,4})\\d*', ~ sprintf("%03d",as.numeric(x)), l, perl=TRUE)` — Wiktor Stribiżew, Oct 08 '18 at 13:30
Please see [How to make a great R reproducible example](https://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example). — Wiktor Stribiżew, Oct 09 '18 at 08:41
Please update the post with what your `preactorDF[["Flight No"]]` is, use `dput`. — Wiktor Stribiżew, Oct 09 '18 at 08:49
The preactorDF has 1.3 million records. dput would be massive. — rj3838, Oct 09 '18 at 09:02
`dput(head(preactorDF[["Flight No"]],10)) c("BA038", "BA038", "BA247", "BA247", "BA198", "BA238", "BA238", "BA057", "BA199", "BA199")'` but this is a small selection and very tidy. other rows have NA in which may be the problem. — rj3838, Oct 09 '18 at 09:18
I cannot help more if you keep the data to yourself. The comment above does not help. Please provide an [MCVE](https://stackoverflow.com/help/mcve). — Wiktor Stribiżew, Oct 09 '18 at 09:21
Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/181538/discussion-between-rj3838-and-wiktor-stribizew). — rj3838, Oct 09 '18 at 09:28

score 0 · Answer 1 · answered Oct 08 '18 at 16:52

0

You may use

> library(gsubfn)
> l <- c("QU1Y", "ZL002", "FX16", "TD8", "BF007P", "VV1395", "HM18743", "JK0001")
> gsubfn('^[A-Z]{2}\\K0*(\\d{1,4})\\d*', ~ sprintf("%03d",as.numeric(x)), l, perl=TRUE)
[1] "QU001Y" "ZL002"  "FX016"  "TD008"  "BF007P" "VV1395" "HM1874" "JK001"

The pattern matches

^ - start of string
[A-Z]{2} - two uppercase letters
\\K - the text matched so far is removed from the match
0* - 0 or more zeros
(\\d{1,4}) - Capturing group 1: one to four digits
\\d* - 0+ digits.

Group 1 is passed to the callback function where sprintf("%03d",as.numeric(x)) pads the value with the necessary amount of digits.

answered Oct 08 '18 at 16:52

Wiktor Stribiżew

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@rj3838 Provide your input data in the question body. – Wiktor Stribiżew Oct 09 '18 at 08:41
I have errors `fred – rj3838 Oct 09 '18 at 08:50
@rj3838 I cannot help you with that since you have not provided reproducible code, the solution above works well with the strings you posted. – Wiktor Stribiżew Oct 09 '18 at 08:51

zero padding regex dependent on length of digits

1 Answers1