When you want to pull information from a table, the Excel VLOOKUP function is a great solution. The ability to dynamically lookup and retrieve information from a table is a game-changer for many users, and you'll find VLOOKUP everywhere.
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And yet, although VLOOKUP is a relatively easy to use, there is plenty that can go wrong. One reason is that VLOOKUP has a major design flaw — by default, it assumes you're OK with an approximate match. Which you probably aren't.
23 things you should know about VLOOKUP When you want to pull information from a table, the Excel VLOOKUP function is a great solution. The ability to dynamically lookup and retrieve information from a table is a game-changer for many users, and you'll find VLOOKUP everywhere. The odds are good; the goods, odd. Two of them associated with a 0 and the other two with a 1. The receiver likewise randomly chooses which kind of polarisation to check for. There are two. View Homework Help - Chapter 4 Questions Enhancing Photos with Image-Editing Software from CAS 50 at Chabot College. 1.Which of the following statements about image editing software is FALSE?a.
This can cause results that look completely normal, even though they are totally incorrect. Trust me, this is NOT something you want to try to explain to your boss, after she's already sent your spreadsheet to management :)
Read below learn how to manage this challenge, and discover other tips for mastering the Excel VLOOKUP function.
1. How VLOOKUP works
VLOOKUP is a function to lookup up and retrieve data in a table. The 'V' in VLOOKUP stands for vertical, which means the data in the table must be arranged vertically, with data in rows. (For horizontally structured data, see HLOOKUP).
If you have a well structured table, with information arranged vertically, and a column on the left which you can use to match a row, you can probably use VLOOKUP.
VLOOKUP requires that the table be structured so that lookup values appear in the left-most column. The data you want to retrieve (result values) can appear in any column to the right. When you use VLOOKUP, imagine that every column in the table is numbered, starting from the left. To get a value from a particular column, simply supply the appropriate number as the 'column index'. In the example below, we want to look up the email address, so we are using the number 4 for column index:
In the above table, the employee IDs are in column 1 on the left and the email addresses are in column 4 to the right.
To use VLOOKUP, you supply 4 pieces of information, or 'arguments':
- The value you are looking for (lookup_value)
- The range of cells that make up the table (table_array)
- The number of the column from which to retrieve a result (column_index)
- The match mode (range_lookup, TRUE = approximate, FALSE = exact)
Video: How to use VLOOKUP (3 min)
If you still don't get the basic idea of VLOOKUP, Jon Acampora, over at Excel Campus, has a great explanation based on the Starbucks coffee menu.
2. VLOOKUP only looks right
Perhaps the biggest limitation of VLOOKUP is that it can only look to the right to retrieve data.
This means that VLOOKUP can only get data from columns to the right of first column in the table. When lookup values appear in the first (leftmost) column, this limitation doesn't mean much, since all other columns are already to the right. However, if the lookup column appears inside the table somewhere, you'll only be able to lookup values from columns to the right of that column. You'll also have to supply a smaller table to VLOOKUP that starts with the lookup column.
You can overcome this limitation by using INDEX and MATCH instead of VLOOKUP.
3. VLOOKUP finds the first match
In exact match mode, if a lookup column contains duplicate values, VLOOKUP will match the first value only. In the example below, we are using VLOOKUP to find a first name, and VLOOKUP is set to perform exact match. Although there are two 'Janet's in the list, VLOOKUP matches only the first:
Note: behavior can change when VLOOKUP is used in approximate match mode. This article explains the topic in detail.
4. VLOOKUP is not case-sensitive
When looking up a value, VLOOKUP does not process upper and lower case text differently. To VLOOKUP, a product code like 'PQRF' is identical to 'pqrf'. In the example below, we are looking for uppercase 'JANET' but VLOOKUP does not distinguish case so it simply matches 'Janet', since that's the first match it finds:
5. VLOOKUP has two matching modes
VLOOKUP has two modes of operation: exact match and approximate match. In most cases, you'll probably want to use VLOOKUP in exact match mode. This makes sense when you want to lookup information based on a unique key of some kind, for example, product information based on a product code, or movie data based on a movie title:
The formula in H6 to lookup year based on an exact match of movie title is:
However, you'll want to use approximate mode in cases where you're not matching on a unique id, but rather you're looking up the 'best match' or the 'best category'. For example, perhaps you're looking up postage based on weight, looking up tax rate based on income, or looking up a commission rate based on a monthly sales number. In these cases, you likely won't find the exact lookup value in the table. Instead, you want VLOOKUP to get you the best match for a given lookup value.
The formula in D5 does an approximate match to retrieve the correct commission:
6. Caution: VLOOKUP uses approximate match by default
Exact and approximate matching in VLOOKUP is controlled by the 4th argument, called 'range lookup'. This name is not intuitive, so you'll just have to memorize how it works.
For exact match, use FALSE or 0. For approximate match, set range_lookup to TRUE or 1:
Unfortunately, the 4th argument, range_lookup, is optional and defaults to TRUE, which means VLOOKUP will do an approximate match by default. When doing an approximate match, VLOOKUP assumes the table is sorted and performs a binary search. During a binary search, if VLOOKUP finds an exact match value, it returns a value from that row. If however, VLOOKUP encounters a value greater than the lookup value, it will return a value from the previous row.
This is a dangerous default because many people unwittingly leave VLOOKUP in it's default mode, which can cause an incorrect result when the table is not sorted.
To avoid this problem, make sure to use FALSE or zero as the 4th argument when you want an exact match.
7. You can force VLOOKUP to do an exact match
To force VLOOKUP to find an exact match, make sure to set the 4 argument (range_lookup) to FALSE or zero. These two formulas are equivalent:
- Cryptography Tutorial
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The Data Encryption Standard (DES) is a symmetric-key block cipher published by the National Institute of Standards and Technology (NIST).
DES is an implementation of a Feistel Cipher. It uses 16 round Feistel structure. The block size is 64-bit. Though, key length is 64-bit, DES has an effective key length of 56 bits, since 8 of the 64 bits of the key are not used by the encryption algorithm (function as check bits only). General Structure of DES is depicted in the following illustration −
Since DES is based on the Feistel Cipher, all that is required to specify DES is −
- Round function
- Key schedule
- Any additional processing − Initial and final permutation
Initial and Final Permutation
The initial and final permutations are straight Permutation boxes (P-boxes) that are inverses of each other. They have no cryptography significance in DES. The initial and final permutations are shown as follows −
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Round Function
The heart of this cipher is the DES function, f. The DES function applies a 48-bit key to the rightmost 32 bits to produce a 32-bit output.
Expansion Permutation Box − Since right input is 32-bit and round key is a 48-bit, we first need to expand right input to 48 bits. Permutation logic is graphically depicted in the following illustration −
The graphically depicted permutation logic is generally described as table in DES specification illustrated as shown −
XOR (Whitener). − After the expansion permutation, DES does XOR operation on the expanded right section and the round key. The round key is used only in this operation.
Substitution Boxes. − The S-boxes carry out the real mixing (confusion). DES uses 8 S-boxes, each with a 6-bit input and a 4-bit output. Refer the following illustration −
The S-box rule is illustrated below −
There are a total of eight S-box tables. The output of all eight s-boxes is then combined in to 32 bit section.
Straight Permutation − The 32 bit output of S-boxes is then subjected to the straight permutation with rule shown in the following illustration:
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Key Generation
The round-key generator creates sixteen 48-bit keys out of a 56-bit cipher key. The process of key generation is depicted in the following illustration −
The logic for Parity drop, shifting, and Compression P-box is given in the DES description.
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DES Analysis
The DES satisfies both the desired properties of block cipher. These two properties make cipher very strong.
Avalanche effect − A small change in plaintext results in the very great change in the ciphertext.
Completeness − Each bit of ciphertext depends on many bits of plaintext.
During the last few years, cryptanalysis have found some weaknesses in DES when key selected are weak keys. These keys shall be avoided.
DES has proved to be a very well designed block cipher. There have been no significant cryptanalytic attacks on DES other than exhaustive key search.