CODEWITHSUNDEEP
rdata.table
Nick
Nick

Reputation: 9061

How to read tab separated file into data.table using fread?

Sample data (emp.data)

Beth  4.00  0
Dan   3.75  0
Kathy 4.00  10
Mark  5.00  20
Mary  5.50  22
Susie 4.25  18

I can read it into a data.frame using read.table, then convert it to data.table:

library(data.table)
df <- read.table("emp.data", col.names = c("Name", "PayRate", "HoursWorked"))
DT <- as.data.table(df, key = HoursWorked)

Calculate the pay (filter out zero hours):

DT[HoursWorked > 0, .(Name, Pay = PayRate * HoursWorked),]

    Name   Pay
1: Kathy  40.0
2:  Mark 100.0
3:  Mary 121.0
4: Susie  76.5

That works fine; however, I consider there's an extra step in converting. Since there's fread() in data.table, why not use it directly?

readDT <- fread("emp.data", header=FALSE, sep="\t")

               V1
1:  Beth  4.00  0
2:  Dan   3.75  0
3: Kathy 4.00  10
4: Mark  5.00  20
5: Mary  5.50  22
6: Susie 4.25  18

 str(readDT)
Classes 'data.table' and 'data.frame':  6 obs. of  1 variable:
 $ V1: chr  "Beth  4.00  0" "Dan   3.75  0" "Kathy 4.00  10" "Mark  5.00  20" ...
 - attr(*, ".internal.selfref")=<externalptr>

The data is recognized as one column; obviously this doesn't work.

Question

How to read this data using fread() properly? (If possible, set the column names as well.)

Upvotes: 12

Views: 10724

Answers (2)

Arun
Arun

Reputation: 118889

This has been fixed recently in the devel version, v1.9.5 (will be soon available on CRAN as v1.9.6):

require(data.table) # v1.9.5+
fread("~/Downloads/tmp.txt")
#       V1   V2 V3
# 1:  Beth 4.00  0
# 2:   Dan 3.75  0
# 3: Kathy 4.00 10
# 4:  Mark 5.00 20
# 5:  Mary 5.50 22
# 6: Susie 4.25 18

See README.md in the project page for more info. fread gained strip.white argument (amidst other functionalities / bug fixes) which is by default TRUE.

Update: it also has col.names argument now:

fread("~/Downloads/tmp.txt", col.names = c("Name", "PayRate", "HoursWorked"))
#     Name PayRate HoursWorked
# 1:  Beth    4.00           0
# 2:   Dan    3.75           0
# 3: Kathy    4.00          10
# 4:  Mark    5.00          20
# 5:  Mary    5.50          22
# 6: Susie    4.25          18

Upvotes: 8

akrun
akrun

Reputation: 887951

Using awk to remove the white spaces and then reading with fread worked for me.

 DT <- fread("awk '{$1=$1}1' emp.data")
 DT 
 #      V1   V2 V3
 #1:  Beth 4.00  0
 #2:   Dan 3.75  0
 #3: Kathy 4.00 10
 #4:  Mark 5.00 20
 #5:  Mary 5.50 22
 #6: Susie 4.25 18

 str(DT)
 #Classes ‘data.table’ and 'data.frame':    6 obs. of  3 variables:
 #$ V1: chr  "Beth" "Dan" "Kathy" "Mark" ...
 #$ V2: num  4 3.75 4 5 5.5 4.25
 #$ V3: int  0 0 10 20 22 18
 # - attr(*, ".internal.selfref")=<externalptr>

I was able to replicate the same problem with the OP's code

 fread("emp.data", header=FALSE, sep="\t")
 #               V1
 #1:  Beth  4.00  0
 #2:  Dan   3.75  0
 #3: Kathy 4.00  10
 #4: Mark  5.00  20
 #5: Mary  5.50  22
 #6: Susie 4.25  18

Upvotes: 6

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